Magnetic resonance imaging apparatus and control method therefor

ABSTRACT

The magnetic resonance imaging apparatus includes: a calculation means for calculating the amount of absorption of electromagnetic waves into the object according to the emission of RF pulses in a part of the object or a bed position where imaging is scheduled; a means for setting imaging conditions, in which the calculated amount of absorption satisfies conditions of the specified value of the amount of absorption of electromagnetic waves, from the relationship between the calculated amount of absorption and the specified value of the amount of absorption of electromagnetic waves; and a bed control device that controls a top plate according to the set imaging conditions.

TECHINCAL FIELD

The present invention relates to a magnetic resonance imaging apparatusand a control method for a magnetic resonance imaging apparatus.

BACKGROUND ART

There is magnetic resonance imaging (hereinafter, referred to as “MRI”)as a technique of imaging and displaying the internal tissue of anobject, such as a human body, and an MRI apparatus using this techniqueis known. In this MRI apparatus, a static magnetic field is applied tothe object from the outside, and a high frequency magnetic field pulse(hereinafter, referred to as an “RF pulse”) that is a high frequencyelectromagnetic wave is further applied. Then, the nuclear spins ofatoms that form the tissue of the object cause the precession, a nuclearmagnetic resonance signal (hereinafter, referred to as an “NMR signal”)generated when the nuclear spins return to a stable state is measured,and the shape or function of a measurement target part of the object,for example, shapes or functions of the head, chest, abdomen, limbs, andthe like are imaged and displayed in a two-dimensional manner or in athree-dimensional manner using the NMR signal.

Images captured by the MRI apparatus are very effective for medicaldiagnosis. Accordingly, these images are widely used when diagnosing thestate of illness or injury. An imaging target when the MRI apparatuscaptures a medical image is a human body as described above, and it isnecessary to assume a state in which there is already a serious problemin health, such as injury or illness.

For this reason, it is necessary to pay close attention to safety. Thereis an international standard on safety “IEC 60601-2-33, 3rd edition”regarding electromagnetic waves used for imaging by the MRI apparatus.According to this international standard, the amount of absorption of RFpulses into the human body per unit time and unit mass is defined as aspecific absorption rate (SAR), the upper limit of the SAR value is set,and imaging should be performed under the imaging conditions in whichthe upper limit is not exceeded. Restrictions on the amount ofirradiation of electromagnetic waves have been demanded so that theelectromagnetic waves exceeding the upper limit of the SAR value are notemitted to the human body, which is an imaging target, in imaging usingthe MRI apparatus. For safety, it is necessary to keep the restrictionsbased on the standard.

An example of a method of keeping the international regulationsregarding the amount of irradiation of electromagnetic waves isdisclosed in PTL 1. The method disclosed in PTL 1 is a method of usingthe MR signal for determining the position of the object on the bed. Inorder to determine the position of the object on the bed, an RF pulse isemitted to the object, an MR signal is detected from the entire body ofthe object, and the position of the object on the bed is determinedbased on the detection result and the output of RF pulses is determinedso as not to exceed the upper limit of the SAR value based on thedetection result.

CITATION LIST Patent Literature

[PTL 1] U.S. Pat. No. 7,834,624

SUMMARY OF INVENTION Technical Problem

In the method disclosed in PTL 1, an MI signal is detected over a widerange of an object placed on the bed, particularly, over the entire bodyof the object as shown in FIG. 3, while moving the object within thegantry of the MRI apparatus, and the position of the object on the bedis determined based on the detected MI signal and the output power ofthe RF pulses is determined so as not to exceed the upper limit of theSAR value.

In this method, it is difficult to improve the accuracy of the estimatedvalue of the SAR value during the imaging of the object. Therefore, itis necessary to increase a safety margin in the determination of theoutput power of RF pulses. On the contrary, as a result of increasingthe safety margin, the output of RF pulses is suppressed lower thannecessary. If the output of RF pulses is made lower than necessary, forexample, there is a risk that the captured image quality will belowered. In addition, if the safety margin is small, the SAR value mayexceed the estimated value of the SAR value, which has been estimated inadvance, during the imaging, and the upper limit of the SAR value may beexceeded. In this case, the imaging should be stopped.

If the imaging is stopped on the way, the working efficiency issignificantly reduced since the imaging operation should be repeated.Therefore, an MRI apparatus capable of estimating the SAR value withhigher accuracy in advance and a control method therefor have beendemanded.

It is an object of the invention to provide an MRI apparatus capable ofestimating the SAR value with high accuracy and a control methodtherefor.

Solution to Problem

A magnetic resonance imaging apparatus of the invention includes: a bedincluding a top plate that moves an object placed thereon; a magneticfield generation means for generating a magnetic field in a space inwhich the object is located; an irradiation coil for irradiating theobject with RF pulses; a means for detecting an NMR signal generated bythe object and imaging the detected NMR signal; an input and outputdevice for inputting or displaying imaging conditions; and a controldevice that calculates an amount of absorption of electromagnetic wavesaccording to emission of the RF pulses to the object based on the inputimaging conditions, determines whether or not the calculated amount ofabsorption satisfies conditions of a specified value of the amount ofabsorption of electromagnetic waves, and performs at least one ofmovement control of the top plate and irradiation control of the RFpulses in accordance with imaging conditions determined to satisfy theconditions of the specified value of the amount of absorption ofelectromagnetic waves, in imaging of the part or in imaging at the bedposition.

Advantageous Effects of Invention

According to the invention, it is possible to obtain an MRI apparatuscapable of estimating the SAR value in imaging with high accuracy and acontrol method therefor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the overall configuration of an MRIapparatus that is an embodiment of the invention.

FIG. 2 is a display screen for inputting or setting the imaging scheduleor imaging conditions.

FIG. 3 is a flowchart for setting the imaging schedule or imagingconditions.

FIG. 4 is a flowchart showing the imaging operation of the MRI apparatusto which the invention is applied.

FIG. 5 is a flowchart showing another embodiment of the flowchart of theimaging operation shown in FIG. 4.

FIG. 6 is an explanatory diagram showing the storage state ofinformation relevant to the calculation of a predicted SAR value or thecalculation of a measured SAR value.

FIG. 7 is an explanatory diagram for explaining a database of W-basicused for the calculation of the predicted SAR value.

FIG. 8 is an explanatory diagram for explaining the database ofW-patient used for the calculation of the measured SAR value.

FIG. 9 is a flowchart for calculating the predicted SAR value.

FIG. 10 is a flowchart for calculating the measured SAR value.

FIG. 11 is a flowchart showing still another embodiment of the flowchartof the imaging operation shown in FIG. 4.

FIG. 12 is a flowchart showing still another embodiment of theembodiment shown in FIGS. 3 and 4.

FIG. 13 is a flowchart showing still another embodiment of theembodiment shown in FIGS. 3 and 4.

FIG. 14 is an explanatory diagram for explaining the display content ofan imaging schedule display portion of a display.

FIG. 15 is a database showing the position information of a standardpart.

FIG. 16 is a flowchart for converting the position of a part of anobject into the moving length of a top plate.

FIG. 17 is an explanatory diagram showing a state in which an object isplaced on the top plate of the bed in the head first direction.

FIG. 18 is an explanatory diagram showing a state in which an object isplaced on the top plate of the bed in the feet first direction.

FIG. 19 is a flowchart for inputting a part to be imaged.

FIG. 20 is a display image on a display provided in a gantry.

FIG. 21 is an explanatory diagram of an input portion provided in thebed.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of an MRI apparatus and a control methodtherefor to which the invention is applied will be described withreference to the diagrams. In the diagrams described below, componentsor steps having the same reference numerals have approximately the sameconfiguration or approximately the same operation, and showapproximately the same effect. Repeated explanation of these componentsor steps will be omitted.

Basic configuration of an MRI apparatus 100

FIG. 1 is a block diagram schematically showing the overallconfiguration of the MRI apparatus 100 that is an embodiment of theinvention. MRI apparatus 100 is an apparatus that captures a tomographicimage of an object 1 placed on a bed 82 using a nuclear magneticresonance (hereinafter, referred to as NMR) phenomenon. The MRIapparatus 100 includes: a magnetic field generating system 30 includinga static magnetic field generating source 20 and a gradient magneticfield generating coil 32; a transmission system 40; a receiving system50; a signal processing system 60 including a central processing unit(hereinafter, referred to as a CPU) 14 and an input and output device90; a bed control device 80 that controls the bed 82; a sequencer 12;and a marker 15. The static magnetic field generating source 20 and thegradient magnetic field coil 32 generate a static magnetic field and agradient magnetic field in the imaging space formed in the centralportion of the gantry.

The object 1 is guided to the imaging space in the gantry in a state ofbeing placed on the bed 82, and, for example, magnetic fields generatedby the static magnetic field generating source 20 and the gradientmagnetic field coil 32 are applied to the object 1, and a high frequencymagnetic field pulse (hereinafter, referred to as an RF pulse) isemitted from an irradiation coil 48 to the object 1. As a result, nucleiof atoms that form the body tissue of a part of the object 1 areexcited, thereby inducing the NMR phenomenon. Nuclei generate an NMRsignal due to the NMR phenomenon, and the NMR signal is received by areceiving coil 52 provided near the object 1. An image is formed by thereceived NMR signal, and is displayed on a display provided in an outputdevice 96 of the signal processing system 60. The output device 96includes not only the display but also a printer or various other outputdevices if necessary.

The magnetic field generating system 30 includes a gradient magneticfield coil 32 for each axis, which is provided to apply a gradientmagnetic field in each of three axial directions of X, Y, and Z axesthat are the coordinate system, that is, the stationary coordinatesystem of the MRI apparatus, and a gradient magnetic field power source34 for driving the gradient magnetic field coil 32 for each axis. Bydriving the gradient magnetic field power source 34 of each gradientmagnetic field coil according to the command from the sequencer 12, agradient magnetic field Gx, Gy, or Gz is applied to the object 1 in theX, Y, or Z axis. At the time of MRI imaging, for example, aslice-direction gradient magnetic field pulse (Gs) is applied in adirection perpendicular to the slice surface, that is, an imagingsection in order to set a slice surface for the object 1, and aphase-encoding-direction gradient magnetic field pulse (Gp) and afrequency-encoding-direction gradient magnetic field pulse (Gf) areapplied in two remaining directions, which are perpendicular to theslice surface and are also perpendicular to each other, in order toencode the position information in each of the directions in the NMRsignal.

The static magnetic field generating source 20 based on the horizontalmagnetic field method that generates a uniform static magnetic field ina body axis direction 2 of the object 1 is used, and a permanent magnettype static magnetic field generating source, a normal conduction typestatic magnetic field generating source, or a superconducting typestatic magnetic field generating source is disposed around the object 1.In addition, the static magnetic field generating source 20 based on thevertical magnetic field method that generates a uniform static magneticfield in a direction perpendicular to the body axis in the space aroundthe object 1 may be used. The basic idea is the same, and an example ofusing the horizontal magnetic field method will be described below as arepresentative example. However, as described above, the application ofthe invention is not limited to the horizontal magnetic field method.

The transmission system 40 emits an RF pulse to the object 1 in order tocause nuclear magnetic resonance in the nuclear spins of atoms that formthe body tissue of the object 1, and includes a high frequencyoscillator 42, a modulator 44, a high frequency amplifier 46, and theirradiation coil 48 that is a high frequency coil. The irradiation coil48 is disposed near the object 1. The RF pulse output from the highfrequency oscillator 42 is amplitude-modulated by the modulator 44 atthe timing according to the command from the sequencer 12, and theamplitude-modulated RF pulse is amplified by the high frequencyamplifier 46 and is then supplied to the irradiation coil 48. As aresult, the RF pulse is emitted to the object 1. The amount ofabsorption of the RF pulse emitted from the irradiation coil 48 into theobject 1 is measured by an SAR measurement unit 70.

The receiving system 50 has a function of detecting an NMR signalemitted by the NMR phenomenon, and includes a receiving coil 52 that isa high frequency coil, a signal amplifier 54, a quadrature phasedetector 56, and an analog-to-digital converter (hereinafter, referredto as an A/D converter) 58. An NMR signal from a part of the object 1that is excited by the RF pulse emitted from the irradiation coil 48 isreceived by the receiving coil 52 disposed near the object 1 and isamplified by the signal amplifier 54, and is divided into two signalsperpendicular to each other by the quadrature phase detector 56 at atiming according to the command from the sequencer 12. Each of the twosignals is converted into digital data by the A/D converter 58, and istransmitted to the signal processing system 60.

The irradiation coil 48 and the gradient magnetic field coil 32 areprovided in the static magnetic field space (not shown) of the staticmagnetic field generating source 20, in which the object 1 is inserted,so as to face the object 1 in the case of the vertical magnetic fieldmethod and so as to surround the object 1 in the case of the horizontalmagnetic field method. In addition, the receiving coil 52 is provided soas to face or surround the object 1. The sequencer 12 is a control meansfor performing control to repeatedly apply RF pulse and a gradientmagnetic field pulse according to a predetermined pulse sequence, andoperates under the control of the CPU 14 of the signal processing system60 and transmits various commands, which are required to collect data ofa tomographic image of the object 1, to the gradient magnetic fieldpower source 34 of the magnetic field generating system 30, thetransmission system 40, or the receiving system 50.

The bed control device 80 moves the bed 82 or transmits the positioninformation of the bed 82 to the CPU 14 based on a moving distancesignal received from the CPU 14. The moving distance signal may begenerated by the input from the input and output device 90, or may begenerated by the operation of a console that is separately provided inthe MRI apparatus 100.

The marker 15 is formed by a device, such as a laser generator, and isattached to the object 1 in order to designate the position of a part,which becomes an imaging target, or the like. The marker 15 generates alaser, and controls the movement of the bed 82 so that the position ofthe marker 15 comes to a predetermined position of the imaging space,for example, the center of the magnetic field, by detecting the laser.Accordingly, it is possible to move the part of the object 1 designatedby the marker 15 to the center of the magnetic field, for example.

The signal processing system 60 operates as a control device thatperforms command or data input processing for various kinds ofoperations or control, processing or control of various kinds of digitaldata, output processing such as display of a processing result, requireddata storage processing, processing for reading stored data, and thelike. For this reason, the signal processing system 60 includes theinput and output device 90, an external storage device 61 such as anoptical disc 62 or a magnetic disc 64 for storing required data, aninternal storage device (hereinafter, referred to as an internal memory)66, and the CPU 14 operating as a control device that performs overallcontrol of the MRI apparatus 100.

For example, when a digitized NMR signal is input from the receivingsystem 50 to the CPU 14 of the signal processing system 60, the CPU 14generates a tomographic image of the object 1 by performing processing,such as signal processing or image reconstruction. In addition, the CPU14 displays the tomographic image on a display 98 of the output device96, and stores the tomographic image or required data in the magneticdisc 64 or the optical disc 62 of an external storage device 61 whennecessary or based on the operation.

The input and output device 90 of the signal processing system 60includes an input device for inputting various kinds of controlinformation including various setting values used in the processing ofthe MRI apparatus 100 or various commands for operating the MRIapparatus 100 and an output device. Although not shown, the input andoutput device 90 includes a communication device for transmission andreception of information including an image to and from other devices orother systems. As the input device, the input and output device 90includes a keyboard 94 and a pointing device 92 including a trackball, amouse, a pad, and a touch panel. As the output device 96, the input andoutput device 90 includes the display 98 or a printer 99, for example.The input means includes a touch panel provided near the output device96, such as the display 98, as the pointing device 92, and is configuredsuch that the operator can direct the control of various processes ofthe MRI apparatus 100 interactively while observing the display of thedisplay 98.

As the input and output device described above as the configuration ofthe input and output device 90, a plurality of sets of input and outputdevices may be provided when necessary. Not only is the input and outputdevice 90 provided in the console of the MRI, but also a part of theinput and output device 90 is provided in the gantry in order to improveworkability. For example, the display 18 operates as a part of theoutput device of the input and output device 90, and is provided in thegantry (not shown). When the operator works near the gantry, it ispossible to display information required for the operation on thedisplay 18 and to input an instruction, a setting value, and the likefrom the display 18 corresponding to the display content.

The display 18 provided in the gantry having a display function or aninput function operates as a part of the input and output device 90, andis connected to the CPU 14 similarly to the input and output device 90so that the display of required information and the acquisition ofoperated input information are performed through the CPU 14. Thisfunction is very convenient for the operator who works near the gantry.Since it is not necessary to go to the location of the console one byone in order to check or input the display content, workability isimproved. In the display 18 provided in the gantry, a display means andan input means are integrally formed, so that an instruction foroperation can be given while observing the display of the display 18provided in the gantry. In addition, the display content of the display18 provided in the gantry and the display content of the display 98 mayoverlap, and input from the pointing device 92 or the keyboard 94 ispossible instead of the input from the display 18 provided in thegantry.

As nuclides to be imaged by the MRI apparatus 100 described above, ahydrogen nucleus (hereinafter, referred to as proton) that is a maincomponent material of the object 1, which is a human, is widely usedclinically. In the MRI apparatus 100 of the present embodiment, theshapes or functions of parts, such as the head, abdomen, and limbs ofthe human body, are imaged in a two-dimensional or three-dimensionalmanner by imaging the information regarding the spatial distribution ofthe proton density or the spatial distribution of the relaxation time ofthe excitation state.

Preparation of Imaging, and Setting of Imaging Schedule or ImagingConditions

Next, the procedure of capturing an MRI image of the object 1 in the MRIapparatus 100 will be described. The MRI apparatus 100 to which theinvention is applied calculates an SAR value from the input objectinformation or from the setting content for imaging and SAR valuecalculation value provided in advance in the MRI apparatus beforeperforming imaging by irradiating the object 1 with RF pulses, and setsimaging conditions so that the calculated SAR value does not exceed thespecified value that is set based on “IEC 60601-2-33, 3rd edition”.Then, imaging is performed by irradiating the object 1 with RF pulses.In this manner, it is possible to effectively prevent a significantreduction in workability due to stopping of the imaging operation, whichoccurs when exceeding the specified value of the SAR value during theexecution of imaging.

FIG. 2 is a setting image 800 that is used to set the imaging scheduleand imaging conditions of the MRI apparatus 100, and is displayed on thedisplay 98. The setting image 800 may be displayed not only on thedisplay 98 but also on the display 18 provided in the gantry. FIG. 3 isa flowchart for setting the imaging conditions satisfying the conditionsof the SAR.

The setting image 800 includes a scan list display portion 810 fordisplaying a list of scan names 152 illustrated in scans A to E, animaging condition display portion 820 for displaying the imagingconditions of the selected scan name 152, an imaging schedule displayportion 870 for displaying the imaging conditions of each scan name inthe form of a list, and a scan order candidate display portion 880 fordisplaying the appropriate scan order determined by calculation. Theimaging condition display portion 820 displays the imaging conditions,and can also be used when changing the displayed conditions or wheninputting new conditions.

For example, a scan position 834 can be changed by selecting and movingthe displayed scan position 834 with a cursor 150. In addition, theconditions of repetition time (TR) 852 can be changed by selecting thenumerical value of the repetition time (TR) 852 with the cursor 150 andinputting a new numerical value. In addition, by performing an inputoperation by designating a target item or a position on the displayimage with the cursor 150, it is possible to input a new value. This isthe same for other portions other than the illustrated item or position.

When a part to be imaged or a position, which is more specific than thepart, is input in order through the input and output device 90, the scanname 152 for the imaging of each part or more specific indicatedposition that has been input is automatically assigned by the signalprocessing system 60, and is displayed in the scan list display portion810 in the input order in the form of a list of scan names Each scanname 152 is assigned to the input part or the indicated position. Thescan name 152 may be assigned to the part without assigning the scanname 152 to the indicated position.

In the present embodiment, however, the scan name 152 is assigned notonly to a part but also to the more specific indicated position whennecessary. Here, it is very convenient in the management of an imagingoperation or in the operation for imaging to assume that the indicatedposition is a stop position where the bed 82 is stopped for imaging. Forexample, when imaging a plurality of imaging places in the head that areslightly away from each other, the bed 82 is moved corresponding to eachimaging place even for the same head that is the same part, so that theposition of the imaging place in the imaging space of the MRI isadjusted for each imaging place. By assigning the scan name 152 for eachstop position of the bed 82, it is possible to set the imagingconditions including the position of the bed 82 for each stop position.In the results of the study of the inventors, the SAR value absorbedinto the object 1 may change considerably for each imaging position.Therefore, in order to manage the SAR value with high accuracy, it ispreferable to assign the scan name 152 for each stop position of the bed82 with the stop position of the bed 82 as the indicated position.

The scan name 152 is assigned to the input part or the stop position ofthe bed 82, and the imaging conditions including the position of the bedare managed by the scan name 152. Therefore, it is possible to performthe writing or reading of the imaging conditions or imaging result ofthe scan name 152, which is selected with the scan name 152 as akeyword, and information regarding the object 1 into or from theexternal storage device 61 or the internal memory 66. Hereinafter, theimaging conditions including the position of the bed are referred to asa scan set. Each scan set is managed by the scan name 152. In a systemincluding the MRI apparatus 100, if the object 1 is specified, it ispossible to read an image, which is the result of imaging, or therelated scan name 152 from the external storage device 61. Therefore, itis possible to read the imaging conditions or the SAR value at that timeby specifying each scan name 152 from the list of the read scan A 152.

The scan name 152 is assigned in order of the input part or indicatedposition and is displayed on the scan list display portion 810, andimaging is performed in the order of display of the scan name 152. Whenthe display order of the scan name 152 is changed by changing thedisplay position by specifying the scan name 152 with the cursor 150,the imaging order is changed so as to follow the new display order.These operations can be performed not only by using the cursor 150 butalso with a finger using a touch panel provided on the display surfaceof the display 98. This is the same for other items.

When one of the scan names shown as a list, for example, the scan A 152is selected using the cursor 150 or the like, a scan set linked to thescan A 152 is read from the internal memory 66 or the external storagedevice 61, and the imaging conditions are displayed in the imagingcondition display portion 820. For a case in which the imagingconditions of the scan A 152 have not yet been input or for an item forwhich the imaging conditions of the scan A 152 have not yet been input,only the item is displayed in a state in which there are no specificimaging conditions. It is possible to input the imaging conditions inblank fields of the imaging condition display portion 820 whennecessary, or it is possible to change the imaging conditions with a newinput operation even if the imaging conditions are already displayed.

The imaging conditions displayed in the imaging condition displayportion 820 are linked to the selected scan name 152, and these aretreated in the associated state in various operations or controltherefor, such as imaging in the MRI apparatus 100, in the linked state.In this specification, a group of a series of related setting conditionsor setting values including the imaging conditions linked to each scanname 152 may be referred to as a scan card, and each scan name 152 maybe referred to as a scan card name. In the MRI apparatus 100, relatedinformation, such as imaging conditions, below the scan card name 152 istreated as a group. In this manner, by specifying each scan name 152,various setting values including the imaging conditions can be easilyread and checked or changed. In addition, it is possible to performwriting into the internal memory 66 or the external storage device 61 orto perform an imaging operation. Therefore, it becomes easy to performcontrol, management, or an imaging operation.

The imaging condition display portion 820 includes: a positioning imagedisplay portion 830 for displaying a positioning image 832 for setting ascan position; an imaging parameter display portion 850 for inputtingand displaying imaging parameters, such as the repetition time (TR) 852for repeatedly applying the RF pulse, an echo time (TE) 854 that is atime until an NMR signal is actually received from the generation of theNMR signal, or a bed position 856 when performing imaging; an SAR valuedisplay portion 840 for displaying a calculated SAR value to bedescribed later; and an imaging start mark 860 for operating the imagingstart.

Position information indicating the bed position 856 is, for example, arelative position from the center of the magnetic field, and may beinput by the operator. Instead of the input of the operator, the signalprocessing system 60 may calculate the movement position of the bed 82from the positioning image, the position of an imaging section to bedescribed later, and the like, so that the position information isautomatically set. Similarly, also for the repetition time (TR) 852 orthe echo time (TE) 854, the calculation result of the signal processingsystem 60 may be input and set. Alternatively, the operator may inputthe repetition time (TR) 852 or the echo time (TE) 854. The imagingstart mark 860 to give a command for starting the operation of imagingis displayed in the imaging condition display portion 820, and a scanoperation for imaging is started according to the conditions set by theimaging parameter display portion 850 by operating the imaging startmark 860.

A positioning image display portion 831 for displaying the positioningimage 832 for setting the scan position 834 or a scan position 836,which is an imaging position, or an image display portion 837 in which atemporary sectional image 838 based on the set scan position 834 or 836is displayed is provided in the positioning image display portion 830.

The positioning image 832 displayed in the positioning image displayportion 831 is an image in which a wide range of the image of the object1 is shown as, for example, a two-dimensional image such as an image ina side view or an image in a plan view (parietal side), or athree-dimensional image, or a one-dimensional image. The scan position834 or the scan position 836 showing the position of the imaging sectionis displayed so as to overlap the positioning image 832. The scanposition 834 or the scan position 836 has a function of setting whichposition of the sectional image (referred to as a slice image) of theobject 1 is to be imaged. For example, the scan position 834 or the scanposition 836 is set while moving the cursor 150 through the pointingdevice 92, such as a mouse or a touch panel, or the keyboard 94.

In addition, it is possible to change the scan position 834 or the scanposition 836 that has already been set, or it is possible to newly addthe position. For example, when the scan position 834 to be moved isselected by the cursor 150 and is moved to a movement target position,the scan position 836 is also moved automatically according to themovement of the selected scan position 834. By performing a settingoperation when the scan position 834 has moved to an appropriateposition, the new moved position becomes a new setting position. Thescan position 836 is also displayed in the newly set position. Thetemporary sectional image 838 of the new scan position 834 or the scanposition 836 is displayed. The positioning image 832 is an image forspecifying the external shape of the object 1 or the positionalrelationship between the bed 82 and the object 1, and is not an imagefor imaging a detailed section. Therefore, the displayed sectional image838 is not a detailed image but a very rough image for checking thesectional image. However, since it is possible to check whether or notthe imaging position has been appropriately set, the positioning image832 is very helpful.

In order to add the scan position 834 or the scan position 836, the scanposition 834 or the scan position 836 can be newly added by designatinga position to be added with the cursor 150 and performing a settingoperation. In contrast, by selecting the scan position 834 or the scanposition 836 that has already been set and performing an erasingoperation, the scan position 834 or the scan position 836 that is setcan be deleted.

In order to check the state of an image captured at the scan position834 or the scan position 836 in advance, when a specific scan positionis selected from a plurality of set scan positions 834 or scan positions836 with the cursor 150, the temporary sectional image 838 at theselected scan position is displayed in the image display portion 837. Inaddition, when a plurality of scan positions are simultaneouslydesignated by the cursor 150, a plurality of temporary sectional images838 are displayed based on the plurality of designated scan positions.

In FIG. 2, an image for positioning (hereinafter, referred to as ascanogram) is displayed as the positioning image 832, and a sectionalimage of the scanogram is displayed in the temporary sectional image 838based on the scan position selected by the cursor 150. When a specificscan name is selected by the cursor 150 as described above, imagingconditions linked to the selected scan name are displayed in the imagingcondition display portion 820, and the set scan position is displayed inthe positioning image display portion 830 of the imaging conditiondisplay portion 820. When a plurality of scan positions of the selectedscan name are set, a plurality of scan positions 834 or a plurality ofscan positions 836 for displaying the scan positions are displayed. Byselecting a specific scan position from the plurality of scan positions834 or the plurality of scan positions 836, it is possible to check thestate of the captured image in advance. Thus, since it is possible tocheck the state of the captured image of the object 1 when imaging basedon the scan list has actually been performed, it is possible to improvethe reliability of imaging.

However, the method of using the scanogram of the object 1 for thesetting of the imaging conditions is an example, and a standard modelimage that is read from the external storage device 61 may be usedinstead of the scanogram. Alternatively, a past image of the object 1may be used. In the case of using a standard model image, if there is adifference between the actual size of the object 1 and the size of amodel image to be used, the set positional relationship may be modifiedand specified by proportional calculation using the ratio of the size ofthe object 1 and the size of the model image.

In FIG. 2, the positioning image 832 or the temporary sectional image838 corresponding to the scan A 152 selected by the cursor 150 isdisplayed in the image display portion 837. By performing display formaking the selected scan name clear so that the relationship of the linkbetween the selected scan name and the positioning image display portion830 can be visually recognized, for example, by changing the color ofthe display to a color different from those for the other scan names,the visual effect is improved. The visual effect is also improved by thedisplay format in which the selected scan A 152 and the imagingcondition display portion 820 are connected as shown in FIG. 2 as anexample (hereinafter, referred to as a tab display).

According to the study of the inventors, it has been found that thevalue of the SAR absorbed into the object 1 is greatly changed in manycases if the part of the object 1 is different. In addition, when thebed 82 is moved to perform imaging since the scan positions areseparated from each other even though the imaging target part is thesame, it has been found that the value of the SAR absorbed into theobject 1 is changed if the bed 82 is moved. For this reason, it isdesirable to determine the value of the SAR by predictive calculationfor each part unit, or more specifically, for each stop position wherethe movement of the bed 82 is stopped for imaging and to set the imagingconditions based on the predicted value of the SAR. By managing thevalue of the SAR by performing predictive calculation of the value ofthe SAR for each stop position of the bed 82, the imaging conditions forimaging at each stop position of the bed 82 can be more appropriatelyset with higher accuracy while maintaining the regulations of the SAR.By setting the scan name 152 so as to correspond to the stop position ofthe bed 82, it is possible to finely set the imaging conditions for eachstop position of the bed 82. For example, it is possible to set theirradiation output of the RF pulse with higher accuracy.

In the embodiment shown in FIG. 2, each scan name 152 displayed in thescan list display portion 810 is automatically set so as to match theinput part or the bed stop position where imaging is performed. This isan example, and the determination conditions of the irradiation outputof the RF pulse are different when the type of an image to be capturedis different even if the bed stop position is the same. Therefore, it isbetter to assign a new scan name if the type of an image to be capturedis different. When the setting conditions in the positioning imagedisplay portion 830 are different or when the setting conditions in theimaging parameter display portion 850 are different, it is desirable toset the imaging conditions by assigning different scan names.

Imaging Condition Setting Operation

The imaging condition setting operation of the MRI apparatus 100 will bedescribed with reference to FIGS. 2 and 3. FIG. 2 is an image displayedon the display 98 in order to set the imaging conditions of the selectedscan name 152 or to display the set imaging conditions, and FIG. 3 is aflowchart showing the content when the signal processing system 60operates to set the imaging conditions. In step S102 in FIG. 3,information regarding the object 1 is input using the keyboard 94 or thepointing device 92. The operation of these inputs can be performed fromthe display 18 provided in the gantry, or can be performed using theinput and output device provided in the bed. Although new informationmay be input, previously input data may be read and a part or all of thedata may be used.

The input information is, for example, information specifying a part tobe imaged, a stop position of the bed 82 for performing scheduledimaging, or the object 1, or information indicating the state of thebody of the object 1.

Although the imaging conditions may be input in the possible range instep S102, the imaging conditions may be collectively input in the nextsteps since all imaging conditions cannot be input in this step. Asinformation of a part to be imaged, for example, there is the head,chest, abdomen, or limbs. Such information is used for the imaging ofthe scanogram performed below or the setting of imaging conditionsincluding imaging parameters.

In the specification of a part, there is a case in which the range of animaging target is too large to be specified. In this case, it ispossible to specify the range of the imaging target at the stop positionof the bed 82. In the next steps, the stop position of the bed 82 may beset from the relationship with the captured scanogram, and the imagingscheduled position may be input by being specified at the stop position.The information specifying the object 1 is a name or the assignednumber, for example. As information indicating the state of the body ofthe object 1, there is a weight, height, age, or sex. The weight orheight of the object 1 can be used to replace the standard referencewith a value corresponding to the object 1. For example, the imagingposition, such as the stop position of the bed 82, is input as datarelative to the standard and is converted into a value corresponding tothe body of the object 1 using the height or the weight, and this can beused as imaging conditions.

The following embodiment will be described on the assumption that partsto be imaged are five parts of “head”, “chest”, “chest”, “abdomen”, and“foot”. The information of a part input in step S102 is also used in theimaging of a scanogram to be performed below. Based on each part thathas been input, the signal processing system 60 sets a scan name forimaging to be described below, creates the list of scan names in theorder of input, and displays the list in the scan list display portion810 of the setting image 800.

In step S104, the object 1 is placed on a top plate 84 of the bed 82,and the top plate 84 is moved to be disposed at a predetermined positionin the gantry of the MRI apparatus 100. The positional relationshipbetween the object 1 and the MRI apparatus 100 is determined so that thereference point of the object 1 matches the reference position of theimaging space. After the positional relationship between the object 1and the MRI apparatus 100 is determined, by moving the top plate 84 ofthe bed 82 accurately using the bed control device 80, it is possible tocontrol the bed 82 so that each part of the object 1 or the scanposition 834 and the scan position 836 comes to a designated position inthe measurement space of the MRI apparatus 100. In step S104, forexample, the object 1 is placed and fixed to the top plate 84 of the bed82, and the marker 15 that emits a laser is fixed to the referenceposition of the part of the object 1, for example, to the center.Position information of the reference position of the part of the object1 designated by the laser from the marke 15 may be transmitted to thebed control device 80 and the top plate 84 of the bed 82 may be movedbased on the position information, so that the reference point of theobject 1 designated by the marker 15 comes to the center of the magneticfield that is the reference position of the magnetic field. In thismanner, it is possible to determine the positional relationship betweenthe position designated by the marke 15 of the object 1 and the MRIapparatus 100.

In step S106, a scanogram for performing a detailed setting of the scanposition 834 or the scan position 836 for imaging is imaged. Thescanogram that is an image for performing a detailed setting of the scanposition does not need to have high resolution, and the resolution forsetting the scan position is sufficient. Therefore, it is possible toset the strength of the emitted RF pulse to be weaker than the strengthof the RF pulse at the time of original MRI imaging. For this reason,since the SAR at the time of imaging of the scanogram is less than theSAR at the time of original MRI imaging, the specified value of the SARis hardly exceeded. However, in order to further improve safety, also inthe imaging of the scanogram, it is checked whether or not the SARexceeds the specified value by following the procedure described below,and then the imaging of the scanogram is performed. As a result, it ispossible to further improve the safety. In addition, it is possible toprevent an abnormal situation, such as the stopping of imaging due tothe SAR value exceeding the setting value during the imaging.

In the imaging of the scanogram in the above step S106, the signalprocessing system 60 determines a distance from the position of eachpart, that is, from the reference point by calculation based on the partinformation for examination that has been input in step S102, andperforms imaging of the scanogram at the calculated position. In theexample described above, the input examination parts are the head,chest, chest, abdomen, and foot, the signal processing system 60determines the position of each part by calculation from the storedinformation of the standard position for the standard height of eachpart and the height of the object 1 input in step S102, and the topplate 84 of the bed 82 is moved through the bed control device 80 so asto move to the positions obtained by the calculation in order of theparts. The imaging of the scanogram of the corresponding part isperformed at each of the bed positions.

The signal processing system 60 stores an image of the two-dimensionalor three-dimensional scanogram of each captured part in the internalmemory 66, the optical disc 62, or the magnetic disc 64.

In steps S112 to S124, the setting of the scan position in each scanname of the scan list is performed using the image of the scanogramcaptured in step S106. The signal processing system 60 assigns a scanname to each part or the bed position previously input in step S102, andstores the list of assigned scan names in an imaging condition storagesection 606 of the internal memory 66. The list of scan names is readfrom the internal memory 66 stored in step S112, and is displayed in thescan list display portion 810 shown in FIG. 2. In step S114, when a scanname is selected from the list of scan names by the operator or by theoperation of the signal processing system 60, if there are imagingconditions that are already set for the selected scan name, the imagingconditions are displayed in the imaging condition display portion 820.Before these conditions are input, the display area is secured, but thedisplay column of the conditions is blank. An item to be input can beselected by designating the display column with the cursor 150.

When the conditions are input to the selected item, the input content isdisplayed, and is set by an operation, such as determination. When ascan name is automatically selected by the signal processing system 60,a scan is selected in a predetermined order. For example, the scan A atthe head of the list is selected first.

In step S116, for a part that is the imaging target of the scan A thatis the selected scan name, here, for the head, a scanogram that has beencaptured and stored in step 106 is read, and is displayed as thepositioning image 832 in the positioning image display portion 830 shownin FIG. 2. In step S122, one scan position to be imaged by the scan A isfirst input to the displayed image 832. This embodiment is an example inwhich a scanogram is used as the image 832 and the input and setting ofthe scan position are performed by displaying the scanogram. However,the use of a scanogram is not essential, and a standard image or patternshowing a part may be used. For example, since the information of theheight or the like of the object 1 is input in step S102, the image of astandard part may be used after being corrected by the features, such asthe height of the object 1, when necessary. There is an effect that itis possible to set the scan position more accurately by simply using thescanogram.

In step S122, one of a plurality of scan positions in the target scanname is input using the pointing device 92 or the keyboard 94. Forexample, by moving the cursor 150 to the scan position using thepointing device 92 or the keyboard 94 and directing the determination,it is possible to set a scan position in a vertical or horizontaldirection from the cursor 150. By inputting a scan position to eachpositioning image 832 that is displayed in a two-dimensional manner, thescan position that is an imaging surface is determined. Then, an imageof the input imaging surface is displayed as the temporary sectionalimage 838. In this manner, one of the scan positions 834 and one of thecorresponding scan positions 836 are input, and one of the scanpositions is set by a determination operation. By repeating thisoperation, it is possible to set a plurality of scan positions that aremanaged in the scan name. Also for a scan position that has already beenset, by selecting the already set scan position with the cursor 150, itis possible to move or delete the selected scan position. In addition,it is possible to perform resetting, such as adding or changing the scanposition, using the pointing device 92 or the keyboard 94.

In step S124, it is determined whether or not all of the required scanpositions have been set for the selected scan name. When all of therequired scan positions have been set, the execution proceeds to thenext step S132. On the other hand, when the setting of the scan positionhas not ended for the selected scan name, step S122 is executed again.Corresponding to the input scan position of the input scan position 834or the scan position 836, the temporary sectional image 838 as an imageis displayed in the image display portion 837 of the positioning imagedisplay portion 830. The case in which each scan name includes one scanposition is rare, and each scan name includes a plurality of scanpositions and these series of scan positions can be managed and treatedas a set.

When it is determined that all of the scan positions managed by theselected scan name have been set in step S124, the input and setting ofparameters for imaging are performed for the scan A that is the selectedscan name in step S132. The imaging parameters input in step S132 arethe repetition time (TR) 852 of high frequency pulses for imagingdescribed above, the echo time (TE) 854, the bed position 856, and thelike. There are various parameters for imaging, and required parametersare input and set in step S132.

When the imaging conditions including the scan position of the scan nameselected in step S132 are roughly input and set, for the confirmation ofsafety, the signal processing system 60 performs predictive calculationof the SAR in order to check whether or not the condition that the SARvalue is equal to or less than the specified value is satisfied in thecase of imaging under the imaging conditions of the selected scan namein step S134. The result of the predictive calculation performed by thesignal processing system 60 is displayed as an SAR value 842 in the SARvalue display portion 840 of the imaging condition display portion 820shown in FIG. 2. In contrast to this, a specified SAR value 844 thatshould not be exceeded is displayed in the SAR value display portion840.

Here, equations for performing the predictive calculation of the SAR areexpressed as (Equation 1), (Equation 2), and (Equation 3).

$\begin{matrix}{{{Predicted}\mspace{14mu} {entire}\mspace{14mu} {body}\mspace{14mu} {{SAR}\left( {W\text{/}{kg}} \right)}} = {W - {{basic}\frac{{Power}\mspace{14mu} {{seq}(W)}}{{object}\mspace{14mu} {weight}\mspace{14mu} {M({kg})}}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \\{{{Predicted}\mspace{14mu} {body}\mspace{14mu} {part}\mspace{14mu} {{SAR}\left( {W\text{/}{kg}} \right)}} = {W - {{basic}\frac{{Power}\mspace{14mu} {{seq}(W)}}{{part}\mspace{14mu} {mass}\mspace{14mu} {of}\mspace{14mu} {body}\mspace{14mu} {in}\mspace{14mu} {irradiation}\mspace{14mu} {range}\mspace{14mu} {m_{p}({kg})}}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack \\{{{Predicted}\mspace{14mu} {head}\mspace{14mu} {SAR}\; \left( {W\text{/}{kg}} \right)} = {W - {{basic}\frac{{Power}\mspace{14mu} {{seq}(W)}}{{head}\mspace{14mu} {mass}\mspace{14mu} {m_{h}({kg})}} \times R_{h}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In (Equation 1), (Equation 2), and (Equation 3), Power seq (W) indicatesPower sequence, and is a value obtained when the signal processingsystem 60 calculates the energy of the RF pulse emitted by theirradiation coil 48 based on the imaging parameters. In addition,W-basic is an SAR absorption rate, for example, a statistical averagevalue of the SAR absorption rates when irradiating each part of a human,who is an object, with RF pulses. The entire body SAR defined by(Equation 1) is a numerical value obtained by dividing the energy ofelectromagnetic waves absorbed into the entire body of the object by theenergy of electromagnetic waves of RF pulses by the mass of the object.The body part SAR defined by (Equation 2) is obtained by dividing theenergy of electromagnetic waves absorbed into a desired part of theobject by the mass of the desired part of the object. The head SARdefined by (Equation 3) is a value obtained by multiplying the entirebody SAR by a head absorption rate Rh and dividing the result by thehead mass.

Here, as described above, the specified SAR value is an SAR upper limitthat should not be exceeded, and this is a value defined by apredetermined average time. Therefore, by increasing the waiting time tobe described later, the time average of the SAR absorption rate isreduced. As a result, since the SAR value calculated by each equation islower than the specified SAR value described above, the prescribedconditions are satisfied.

The details of the predictive calculation of the SAR using (Equation 1),(Equation 2), and (Equation 3) will be described below. The predictivecalculation result of the SAR based on (Equation 1), (Equation 2), and(Equation 3) is displayed as the SAR value 842 in the SAR value displayportion 840. When the predictive calculation result of the SAR exceedsthe specified SAR value 844, a warning 846 is displayed in the SAR valuedisplay portion 840, and a scan name at this time is displayed in awarning column 848. The warning of the warning column 848 continues tobe displayed even after the selected scan name is switched to anotherscan name Therefore, when a plurality of scan names are warning targets,the plurality of scan names are displayed in the warning column 848 forwarning. On the other hand, the display of the warning 846 is performedfor the selected scan name, and no warning is displayed in the warning846 when a newly selected scan name is not a warning target. The SARvalue 842 is displayed corresponding to the selected scan name and thespecified SAR value 844 is also displayed corresponding to the selectedscan name, and the warning 846 is displayed under the conditions inwhich the SAR value 842 exceeds the specified SAR value 844.

The signal processing system 60 determines whether or not eachpredictive calculation result calculated in step S134 exceeds thespecified SAR value 844 provided corresponding thereto by executing stepS136. When at least one of the predictive calculation results exceedsthe specified SAR value 844 provided corresponding thereto, the signalprocessing system 60 executes step S138 to display the warning 846 inthe SAR value display portion 840 shown in FIG. 2 and display the targetscan name in the warning column 848 of the scan list display portion810. In this case, imaging parameters or imaging conditions includingthe scan position are reset so that a 6-minute average and a 10-secondaverage of the predictive calculation results do not exceed thespecified SAR value 844.

For the resetting of imaging parameters or imaging conditions includingthe scan position, the signal processing system 60 executes steps S122and S132 again. Here, it is possible to reduce the SAR value by reducingthe number of imaging shown at the scan position 834 or the scanposition 836 or by changing imaging parameters in step S132, and newimaging conditions are input and set. Then, the predictive calculationof the SAR is performed again in step S134. Then, in step S136, it isdetermined whether or not the predictive calculation result under thenewly input imaging conditions exceeds the corresponding specified SARvalue. Thus, it is possible to determine the imaging conditions underthe condition that the specified SAR value 844 is not exceeded.

When it is determined that the predictive calculation result does notexceed the specified SAR value in step S136, the execution of the signalprocessing system 60 proceeds to step S139 in which the input imagingconditions are set and the corresponding warning is eliminated when awarning has been issued in the past in step S138 and the warning isdisplayed in the warning column 848 or in the warning 846. When theoperator selects another scan name 152 in a state in which a warning isdisplayed in the warning column 848, the procedure from step S116 isperformed for the newly selected scan name 152. In this case, theimaging conditions regarding the scan name 152 for which the warning isdisplayed are improved, and the display of the warning is not eliminatedas long as the predictive calculation result exceed the specified SARvalue. Therefore, safety regarding the specified SAR value 844 ismaintained.

The above explanation has been given with the selected scan A as arepresentative example. However, it is determined whether or not theimaging conditions have been set for all of the scan names displayed inthe scan list display portion 810 in step S140, and the execution of thesignal processing system 60 proceeds from step S140 to step S114 whenthere is a scan name for which no imaging conditions are set. Then, ascan name for which the imaging conditions are to be input is selected,the input of imaging conditions and the predictive calculation of theSAR under the input imaging conditions are performed again, and theimaging conditions are set under the condition that the predictivecalculation result of the SAR does not exceed the specified SAR value844. In this manner, imaging conditions are set for each scan namedisplayed in the scan list display portion 810. Then, the execution ofthe signal processing system 60 proceeds to the flowchart of the imagingoperation described in FIG. 4. When there is the scan name 152 for whicha warning is displayed in the warning column 848, the execution proceedsfrom step S140 to step S114 in which the scan name 152, for which awarning is displayed in the warning column 848, is selected, and imagingconditions in which the predictive calculation result does not exceedthe specified SAR value are set. The scan position or imaging conditionsmanaged by each scan name are used as a scan card, and each scan name isstored and managed as a unit of a file in the internal memory 66, theoptical disc 62, and the magnetic disc 64.

When the operator wants to change the scan position or the imagingparameters, the operator selects a scan name displayed in the scan listdisplay portion 810 by operating the cursor 150 regardless of theexecution position of the above flowchart shown in FIG. 3. Then, theimaging conditions of the selected scan name are displayed in theimaging condition display portion 820. In addition, it is possible tochange the already set imaging conditions by selecting the targetimaging conditions with the cursor 150. After changing the imagingconditions, the SAR value is calculated under the changed imagingconditions in step S134, and it is determined whether or not thepredictive calculation result of the SAR exceeds the specified value instep S136. When it is determined that the predictive calculation resultdoes not exceed the specified SAR value in step S136, newly changedimaging conditions are set in step S139. In addition, when a warning hasbeen issued previously in step S138 and the warning is displayed in thewarning column 848, the warning is eliminated.

As described above, it is possible to perform the predictive calculationof the SAR and to set the imaging conditions so that the predictivecalculation result does not exceed the specified value of the SAR.Therefore, safety is further improved. In addition, since it is possibleto prevent the occurrence of an abnormal situation in which the SARvalue exceeds the specified value of the SAR during actual imaging, itis possible to prevent a situation, such as the stopping of imaging dueto the occurrence of the abnormal situation.

FIG. 4 is a flowchart showing the imaging operation of the MRIdescribed. When the imaging start mark 860 displayed in the settingimage 800 shown in FIG. 2 is operated or when the imaging start key ofthe input and output device 90 is selected, the signal processing system60 executes step S302 in FIG. 4, and the MRI apparatus 100 starts theimaging operation. In step S304, the signal processing system 60 selectsautomatically a scan name at the head displayed in the scan list displayportion 810. The order of the scan name displayed in the scan listdisplay portion 810 indicates an imaging order, and the scan namelocated at the head is selected first by the signal processing system60. The signal processing system 60 reads the scan card of the selectedscan name, and controls the bed 82 based on the imaging conditions ofthe read scan card in step S306. The control of the bed 82 is performedby transmitting a control command to the bed control device 80 from thesignal processing system 60. The top plate 84 of the bed 82 iscontrolled according to the imaging conditions so that the first imagingpart of the object 1 is located, for example, at the center of thegradient magnetic field that is the reference position of the imagingspace.

Then, in step S308, RF pulses based on the set imaging conditions areemitted from the irradiation coil 48. Based on the emitted RF pulses,the SAR measurement unit 70 calculates the SAR absorption rate of theindividual object 1 by measurement in step S312. The SAR absorption rate(hereinafter, referred to as W-patient) of the individual object 1 thathas been calculated based on the measurement is further stored in theinternal memory 66 or the optical disc 62 in step S312, and is stored inthe magnetic disc 64 when necessary. Here, the SAR measurement unit 70is a device that calculates a more accurate W-patient corresponding tothe object 1. There is no need to measure the W-patient itself as ameasurement value, and any device that calculates the W-patient usingthe physical quantity measured based on the measured object 1 may beused.

In step S314, based on the W-patient, the signal processing system 60calculates an SAR value (referred to as a measured SAR value) using thefollowing (Equation 4), (Equation 5), and (Equation 6). The measured SARvalue is calculated, and it is determined whether or not the calculatedmeasured SAR value exceeds the specified SAR value in step S316. Basedon the imaging schedule and the W-patient that have been input,predictive calculation of the measured SAR value to be executed later isperformed in step S314, and it is determined whether or not the measuredSAR value obtained by the predictive calculation exceeds the specifiedvalue of the SAR in step S316. The SAR measurement unit 70 measures theW-patient based on the RF pulses emitted for the imaging of the selectedpart, and the signal processing system 60 calculates the measured SARvalue using the measured W-patient in step S314. However, when theW-patient of the target part is not present or when the W-patient of thetarget bed position L is not present, W-patient that is close in termsof a position, among the W-patient that is already present, is selectedand the measured SAR value is calculated based on the imaging schedule,such as the imaging conditions, in step S314. Hereinafter, thecalculation of the SAR value using the W-patient will be referred to asmeasured SAR value calculation. In addition, the calculation result willbe referred to as a measured SAR value.

When the measured SAR value exceeds the specified value of the SAR, theexecution of the signal processing system 60 proceeds to step S320 tostop the imaging operation. When it is determined that the measured SARvalue (step S314) calculated using the W-patient in step S312 does notexceed the specified value of the SAR, step S332 is executed to executethe scheduled imaging operation. There is a case in which the same scanposition is repeatedly imaged even though this is a special case. Inthis case, the execution returns again from step S334 to step S314 torepeat the imaging in the same procedure.

Then, the process returns from step S336 to step S304 in which the nextscan name described in the scan list display portion 810 is selected,the imaging operation is similarly repeated, and the imaging of theselected scan name is performed. After completing the imaging for all ofthe scan names described in the scan list display portion 810 byrepeating the imaging in the above-described procedure for all of thescan names described in the scan list display portion 810, the signalprocessing system 60 determines the end of the imaging in step S336, andthe signal processing system 60 performs processing for ending theimaging of the MRI in step S338 to end the series of imaging operations.

In the flowchart shown in FIG. 4, the signal processing system 60calculates a measured SAR value based on the W-patient based on themeasurement in step S314, determines whether or not the calculationresult of the measured SAR value exceeds the specified SAR value, andstops the imaging operation of the MRI when the calculation result ofthe measured SAR value exceeds the specified SAR value or when it ispredicted that the specified value will be exceeded in a future imagingoperation. Through this operation, it is possible to further improvesafety. In addition, it is possible to reduce the waste of imagingoperation.

Through the predictive calculation of the SAR described in the flowchartof FIG. 3, it is predicted whether or not there is a possibility thatthe SAR value will exceed the specified value during the actual imagingoperation. When there is a possibility that the SAR value will exceedthe specified value, it is possible to avoid wasteful imaging operationthat the imaging operation should be stopped from the relationship ofthe SAR by changing the imaging conditions. In addition, by calculatingthe measured SAR value using the W-patient described in FIG. 4, it ispossible to perform the predictive calculation of the SAR value withvery high accuracy before the actual imaging operation. In addition,even if the imaging operation has started, it is possible to determinein the early stage and with very high accuracy whether or not the SARvalue will exceed the specified SAR value in the imaging operation to beperformed from now. This improves safety, and it is possible to preventwaste, such as the stopping of the imaging operation.

The measured SAR value is calculated from the W-patient according to theirradiation of RF pulses for imaging based on the imaging conditions,and measured SAR monitoring, which is for monitoring whether or not themeasured SAR value that has been calculated with high accuracy exceedsthe specified SAR value, is performed while performing the imagingoperation as described in FIG. 4. By performing the monitoring so thatthe measured SAR value for the object 1 does not exceed the specifiedSAR value, the final safety is maintained. In the embodiment describedin FIG. 4, the operation of imaging the object 1 and the operation ofmonitoring the measured SAR value are included in a series offlowcharts. The operation of imaging the object 1 and the operation ofmonitoring the measured SAR value may be independently performed byprograms that are separately executed. By performing the imagingoperation and the SAR monitoring operation in FIG. 4 in separatedifferent programs, the SAR monitoring operation can be performed in astate in which the SAR monitoring operation is hardly restricted by theimaging operation. Therefore, it is possible to further improve theeffect described above. The operation will be described with referenceto the flowchart shown in FIG. 5. Steps having the same referencenumerals as the reference numerals described in FIG. 4 showapproximately the same operation, and show approximately the sameeffect. Explanation of the steps having reference numerals that havealready been described will be omitted.

The flowchart shown in FIG. 5 shows the operation based on an imagingprogram 360 for performing an imaging operation based on the scan listdescribed in the scan list display portion 810 in FIG. 2, a monitoringprogram 370 for performing the above-described SAR monitoring, and amanagement program 350 for managing the imaging program 360 or themonitoring program 370. These programs are stored in a storage sectionof the internal memory 66 of the signal processing system 60 or anexternal storage device, for example, a storage section of the magneticdisc 64 together with various programs for operating the signalprocessing system 60 described with reference to FIG. 2. By theexecution of the imaging program 360 by the signal processing system 60,steps S302 to S308 and steps S332 to S338 are executed.

Since the basic operation of steps S302 to S308 and steps S332 to S338has already been described, the detailed explanation thereof will beomitted. In step S304, scan names for imaging are sequentially selectedfrom the list of scan names assigned corresponding to the imaging targetpart or the bed position where imaging is to be performed. In step S306,the imaging conditions of the selected scan name selected are searchedfor, and the bed 82 is controlled. In step S308, RF pulses are emittedto perform imaging. After all imaging operations at the scan positionsin the selected scan name are completed, the execution of the signalprocessing system 60 proceeds from step S336 to step S304 to select ascan name for the next imaging in step S306. After the signal processingsystem 60 executes steps S308 and S332 to complete the imaging at allscan positions in the selected scan name, a scan name for the nextimaging is selected in step S304. When the imaging operation for allscan names registered in the list of scan names has been completed asdescribed above, the signal processing system 60 performs processing forending the imaging in step S338, so that the imaging operation is ended.

The signal processing system 60 executes the monitoring program 370,which operates separately from the imaging program 360, and is formonitoring whether or not the measured SAR value exceeds the specifiedSAR value, thereby executing step S352 or steps S312 to S318 andexecuting step S320. The execution of the imaging program 360 or themonitoring program 370 is controlled by system software 350. The systemsoftware 350 is, for example, an operating system (OS), and managesvarious kinds of application software for controlling the hardwareprovided in the MRI apparatus 100 or for performing various kinds ofoperation or monitoring and controls the start, execution, or the likeof each application software. The system software 350 is stored in astorage section of the internal memory 66 of the signal processingsystem 60 or a storage section of the external storage device 61.

When the operator operates the imaging start mark 860 displayed in thesetting image 800 described in FIG. 2 or operates the imaging start keyprovided in the input and output device 90, the system software 350starts the imaging program 360 as corresponding application softwarebased on this operation, and the signal processing system 60 executesstep S302. The system software 350 starts the imaging program 360through the starting means 352 in response to the operation of theoperator, and the starting means 354 starts the monitoring program 370repeatedly at predetermined periods. In the monitoring program 370, whena scan name described in the scan list display portion 810 is specifiedin step S304 of the imaging program 360, the monitoring program 370receives information on the specified scan name in step S352. Based onthe received scan name information, the monitoring program 370 sets thescan name received in step S304 as a target scan name for which themeasured SAR value is to be further calculated in step S352. The scanname receiving method can be realized, for example, by writing theinformation of the scan name selected in step S304 in the specificaddress of the internal memory 66 using the imaging program 360 andreading the selected scan name from the specific address in step S352 ofthe monitoring program 370.

The W-patient that the SAR measurement unit 70 outputs according to theirradiation of RF pulses from the irradiation coil 48 in step S308 ofthe imaging program 360 is repeatedly acquired in step S312 of themonitoring program 370, and the measured SAR value is calculated usingthe W-patient in step S314. In addition, according to the future imagingschedule and the imaging conditions, predictive calculation regardingthe measured SAR is performed using the W-patient in step S314.

In step S316, it is determined whether or not the calculation result ofthe SAR in step S314 or the predicted calculation result of the SAR instep S314 exceeds the specified SAR value. When the calculation resultof the SAR in step S314 or the predicted calculation result of the SARin step S314 does not exceed the specified SAR value, the execution ofthe signal processing system 60 proceeds from step S316 to step S318,and the execution of the monitoring program 370 is ended. On the otherhand, when the calculation result or the predicted calculation result ofthe measured SAR value in step S314 exceed the specified SAR value, thesignal processing system 60 executes step S320 and then executes stepS318 to end the execution of the monitoring program 370. The monitoringprogram 370 is repeatedly executed at very short periods by the systemsoftware 350. Accordingly, the calculation in step S314 is repeatedlyperformed, and monitoring regarding whether or not the measured SAR ofthe calculation result exceeds the specified SAR value is repeatedlyperformed in step S316. Therefore, in the earlier phase, it is possibleto determine whether or not the measured SAR exceeds the specified SARvalue.

Database Used in the Calculation of a Predicted SAR Value or a MeasuredSAR Value

Next, the calculation of the predicted SAR described in step S134 ofFIG. 3 or the calculation of the measured SAR value described in stepS312 of FIGS. 4 and 5 will be described. FIG. 6 is a block diagramshowing the storage state of information relevant to the calculation ofthe predicted SAR value or the calculation of the measured SAR value.The external storage device 61 stores information including variousdatabases required for the imaging operation of the MRI apparatus 100.Object information and various kinds of information used as imagingconditions are transmitted from the external storage device 61, whennecessary, to the internal memory 66. However, even if the aboveinformation is not transmitted to the memory 66 in particular, readingor writing may be performed for the external storage device 61. However,as an example, the following explanation will be given on the assumptionthat the related information is transmitted to the internal memory 66.

The internal memory 66 acquires various databases related to the object1, software, or other pieces of information from the external storagedevice 61 and stores them, and writes and stores the stored information,databases, or the like into the external storage device 61 whennecessary. Examples of the database include a database DB1 of W-basicshown in FIG. 7, which is data of the statistical average value of theSAR absorption rate when emitting the RF pulse, and a database DB2 ofW-patient shown in FIG. 8, which is a database of the measured SARabsorption rate that is calculated by measurement by the SAR measurementunit 70 based on the RF pulse that is actually emitted to the object 1.

The major feature of the database DB1 shown in FIG. 7 or the databaseDB2 shown in FIG. 8 is that the W-basic or the W-patient that is dataincludes data corresponding to each part or each stop position of thebed 82 for imaging. The database DB1 shown in FIG. 7 includes an item ofpart information 610, an item of bed position information 612 that isthe stop position of the bed at which the movement of the top plate 84is stopped for imaging, an item of W-basic information 614 indicatingthe SAR absorption rate of the average person, and an item of headabsorption rate Rh information 616 indicating the SAR absorption rate ofthe head of the average person.

Data Wbb1 to Wbb13 of the W-basic information 614 shown in FIG. 7, whichis data of the statistical average value of the SAR absorption rate, isstored corresponding to each part or each stop position of the bed 82for imaging. The data Wbb1 to Wbb13 is values that are calculated, asaverage values of the measurement values of the SAR absorption ratecorresponding to each part or the stop position of the bed 82 forimaging, based on the measurement of many standard people. Bed positionsL1 to L13 indicating the stop position of the bed 82 are values obtainedby averaging the measured values of the bed position of each person.Therefore, when using the data Wbb1 to Wbb13, proportional calculationbased on the personal height of the object 1 to be imaged is performed,and the data of the bed positions L1 to L13 is used after beingconverted into a value matching the physique of the individual object 1.From the database DB1, the W-basic information 614 can be searched forwith the part information 610 or the bed position information 612 as asearch parameter of the database DB1. In addition, the head absorptionrate Rh information 616 is average data of the absorption rate Rh whenthe high frequency energy of the RF pulse is absorbed by the headcorresponding to each stop position of the bed 82, and can be similarlyread by search using the part information 610 or the bed positioninformation 612 as a search parameter.

In the present embodiment, the data Wbb 1 to Wbb 13 that forms theW-basic information 614 is stored as a value corresponding to each partor each bed position. When the W-basic information 614 is set as datafor a wide region instead of data corresponding to each part or each bedposition, the error becomes very large. In the measurement results ofthe inventors, the values of the data Wbb1 to Wbb13 corresponding toeach part or each stop position are significantly different according tothe part or the bed position. When pieces of data in which parts or thestop positions of the bed 82 are different are compared with each other,there may be a severalfold difference between the values.

For this reason, in the case of using the SAR value that is calculatedusing the average SAR value corresponding to the wide region for which apart or the stop position of the bed 82 is not specified, it can beconsidered to have a very large error depending on the imaging position.When using the SAR value with large error, it is necessary to set a verylarge safety margin when determining the imaging conditions using thepredicted SAR value obtained by calculation. Accordingly, it isdifficult to set the appropriate RF pulse output. In addition, apossibility increases that an abnormal situation, in which the SAR valueexceeds the specified value during the actual imaging, will occur andthe imaging should be stopped.

The database DB2 shown in FIG. 8 includes part information 620 forstoring the data of a part to be imaged, bed position information 622that is the stop position of a bed to be imaged, W-patient information624 that is data of the SAR absorption rate measured corresponding tothe bed position, and head absorption rate Rh information 626 that isdata of the SAR absorption rate measured for the head of the object 1.

Data Wp1 to Wp13 of the W-patient shown in FIG. 8, which is data of theSAR absorption rate measured for the object 1, is provided correspondingto each part or each stop position of the bed 82 for imaging, as in thecase shown in FIG. 7. The data Wp1 to Wp13 is the values of the SARabsorption rate unique to the object 1, which have been measured by theSAR measurement unit 70 by actually emitting RF pulses from theirradiation coil 48 in each part or the stop position of the bed 82 forimaging. Bed positions L1 to L13 indicating the stop position of the bed82 are values of the stop position of the bed 82 for a standard person.Therefore, when using the data Wp1 to Wp13, proportional calculationbased on the height of the object 1 to be used is performed, data of thebed positions L1 to L13 matching the physique of the object 1 iscalculated, and the calculation result is used. However, in the databaseDB2 described in FIG. 8, values unique to the object 1 to be imaged maybe set as the values of the bed positions L1 to L13, instead of theaverage value. In addition, for the head, data of the absorption rate Rhat which the high frequency energy of RF pulses is absorbed into thehead is stored corresponding to each stop position of the bed 82.

The internal memory 66 further includes an imaging condition storagesection 606 and an object information storage section 604 regarding theobject 1, and imaging conditions that are input and set are stored inthe imaging condition storage section 606. Personal information, such asthe stored name, or information regarding the body, such as weight orheight, is stored in the object information storage section 604regarding the object 1. Imaging conditions stored in the internal memory66 are further stored in an imaging condition storage section 607 of theexternal storage device 61, and object information regarding the object1 is stored in an object information storage section 605 of the externalstorage device 61 when necessary. The database DB1 or DB2 is stored inthe external storage device 61. When data is modified, added, or newlycreated in the internal memory 66, the data is stored after beingwritten into the external storage device 61 from the internal memory 66when necessary. In addition, in the external storage device 61,necessary programs are stored, and programs for executing the flowchartsdescribed in this specification are also stored.

Calculation of the Predicted SAR Value

The details of step 134 described in FIG. 3 will be described withreference to the flowchart in FIG. 9. This flowchart shows an operationperformed by the signal processing system 60. In step S412, the signalprocessing system 60 calculates the energy Power seq (W) of RF pulsesemitted by the irradiation coil 48 based on the imaging conditions thatare input and stored in the imaging condition storage section 606 of theinternal memory 66. Then, in step S414, W-basic for entire body SAR thatis a standard value stored in the database DB1 is searched for with apart or the bed position L as a search parameter. Even if the same valueis used for W-basic for entire body SAR, W-basic for part SAR, andW-basic for head SAR without the above-described detailed division intothe W-basic for entire body SAR, the W-basic for part SAR, and theW-basic for head SAR, it is possible to obtain the predicted SAR value.However, since it is possible to read the W-basic for entire body SAR,the W-basic for part SAR, and the W-basic for head SAR based on a partor the movement stop position of the bed 82 herein, it is possible tocalculate the predicted SAR value with very high accuracy.

Here, a representative example of searching for the W-basiccorresponding to (Equation 1), (Equation 2), or (Equation 3) and usingit will be described. In step S416, the weight W of the object 1 inputin step S 102 in FIG. 3 is read from information 604 regarding theobject 1 in the internal memory 66. In step S418, the operation of theabove-described (Equation 1) is performed, and the value of thepredicted entire body SAR (W/kg) is obtained by calculation. Thus, thesignal processing system 60 calculates the predicted entire body SAR(W/kg) through steps S412 to S418. The calculated predicted entire bodySAR (W/kg) is displayed in the SAR value display portion 840 shown inFIG. 2 and is stored in the imaging condition storage section 606 of theinternal memory 66 in step S418. Similarly, in step S422, W-basic forSAR of a part or the bed position to be imaged is searched for from thedatabase DB1 with the part or the bed position as a search parameter. Inaddition, the mass mp of the part to be imaged is calculated from theweight of the object 1. In step S426, the operation of (Equation 2) isperformed, and the signal processing system 60 calculates the predictedbody part SAR. Steps S422 to S426 are a procedure executed in order thatthe signal processing system 60 calculates the predicted body part SAR,and the calculation result is displayed in the SAR value display portion840 and is stored in the imaging condition storage section 606 of theinternal memory 66.

A predicted head SAR value is calculated by the execution of steps S432to S438 by the signal processing system 60, and the calculation resultis displayed and stored. First, in step S432, the W-basic for headstored in the database DB1 is obtained by search with a part or the bedposition as a search parameter. In step S434, the mass mh of the head iscalculated from the input weight W. In addition, the head absorptionrate Rh is obtained by searching from the database DB1 with the part orthe bed position as a search parameter, and the operation of (Equation3) is performed in step S438. The predicted head SAR is obtained by thiscalculation, and is displayed in the SAR value display portion 840 shownin FIG. 2 and is stored in the imaging condition storage section 606 ofthe internal memory 66 shown in FIG. 8.

By executing the flowchart shown in FIG. 9 in this manner by the signalprocessing system 60, the operation of (Equation 1), (Equation 2), or(Equation 3) is performed. The calculation result is displayed as theSAR value 842 in the SAR value display portion 840 shown in FIG. 2. Thesignal processing system 60 determines whether or not the SAR value 842exceeds the specified SAR value 844 by executing step S136 in FIG. 3.The subsequent operation of the signal processing system 60 is the sameas described with reference to FIG. 3.

Calculation of the Measured SAR Value Using Measured W-patient

The details of step S314 described in FIG. 4 or 5 will be describedbelow. The SAR measurement unit 70 measures the energy absorption stateof RF pulses that are high frequency pulses that have been emitted fromthe irradiation coil 48, calculates the absorption rate W-patientactually absorbed into the object 1 based on the measurement value, andstores it as the database DB2. Corresponding to each part orcorresponding to each movement stop position of the bed 82, as describedin FIG. 7, data of the W-patient based on the measurement value isstored in the internal memory 66 as the database DB2, and is furtherstored, for example, in the magnetic disc 64 or the optical disc 62 thatis an external storage device. In the present embodiment, not only doesthe value of the W-patient correspond to a part, but also data of theW-patient measured corresponding to each stop position when moving thebed position is stored since the scan position differs in each part.Therefore, there is an effect that the more accurate measured SAR valueis obtained.

The operation when the signal processing system 60 calculates a measuredSAR value by executing step S314 described in FIG. 4 or step 314described in FIG. 5 will be specifically described with reference toFIG. 10. Here, equations for calculating the measured SAR value based onmeasurement are expressed as (Equation 4), (Equation 5), and (Equation6).

$\begin{matrix}{{{Measured}\mspace{14mu} {entire}\mspace{14mu} {body}\mspace{14mu} {{SAR}\left( {W\text{/}{kg}} \right)}} = {W - {{patient}\frac{{Powerseq}(W)}{{object}\mspace{14mu} {weight}\mspace{14mu} {M({kg})}}}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack \\{{{Measured}\mspace{14mu} {body}\mspace{14mu} {part}\mspace{14mu} {{SAR}\left( {W\text{/}{kg}} \right)}} = {W - {{patient}\frac{{Power}\mspace{14mu} {{seq}(W)}}{{part}\mspace{14mu} {mass}\mspace{14mu} {of}\mspace{14mu} {body}\mspace{14mu} {in}\mspace{14mu} {irradiation}\mspace{14mu} {range}\mspace{14mu} {m_{p\;}({kg})}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack \\{{{Measured}\mspace{14mu} {head}\mspace{20mu} {{S{AR}}\left( {W\text{/}{kg}} \right)}} = {W - {{patient}\frac{{Power}\mspace{14mu} {{seq}(W)}}{{head}\mspace{14mu} {mass}\mspace{14mu} {m_{h}({kg})}} \times R_{h}}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

Here, the W-patient is an absorption rate obtained by the calculation ofthe SAR measurement unit 70 from the measurement value described above.Power seq (W), part mass mp, head mass mh, and head absorption rate Rhare approximately the same as described in (Equation 1), (Equation 2),or (Equation 3).

In the flowchart shown in FIG. 10, in step S442, the signal processingsystem 60 reads imaging conditions that are previously input and storedin the imaging condition storage section 606, and calculates the energyPower seq (W) of RF pulses emitted by the irradiation coil 48 based onthe imaging conditions. When the Power seq (W) previously calculated bythe execution of the flowchart shown in FIG. 3 or the like is stored, itis possible to use the result.

Steps S443 to S445 are a flowchart for performing the operation of(Equation 4). In step S443, for a part for which a measured SAR value isto be calculated, it is checked whether or not the W-patient, which isthe absorption rate of RF pulses that is calculated based on themeasurement value, is stored. When the W-patient based on themeasurement is present in the database DB2, the W-patient is read fromthe database DB2 by search in step S444, and is used for the operationof (Equation 4). As shown in FIG. 7, the W-patient based on themeasurement can be searched for with a part as a search parameter orwith the bed position L, that is, a position where the object 1 isplaced as a search parameter. In the present embodiment, since theW-patient based on the measurement is stored with not only a part butalso the bed position L as a search parameter, it is possible to storethe W-patient suitable for an imaging part. In addition, since it ispossible to use the W-patient having the bed position L as a searchparameter, it is possible to improve the calculation accuracy of themeasured SAR value.

Therefore, the margin of the imaging conditions can be appropriatelyset. As a result, since the appropriate imaging conditions, especially,the irradiation energy of RF pulses can be appropriately set, thequality of a captured image is further improved.

When the W-patient of the target part or the bed position has not beenmeasured, that is, when the corresponding W-patient has not yet finishedthe database DB2, the W-patient of a part near the target part or a bedposition near the target bed position is read by search in step S446.Although the read W-patient is a value for the different part or thedifferent bed position L, it is possible to consider an individualdifference for the standard value of the object 1 by using the readW-patient as it is. Therefore, the accuracy of the predicted SAR valueis further improved by using the measured SAR value obtained bycalculation. In addition, it is possible to further improve the accuracyby correcting the value of the different part or the W-patient for thedifferent bed position L in step S447 instead of using the value of thedifferent part or the W-patient for the different bed position L as itis and using the corrected W-patient.

In step S445, the signal processing system 60 performs the operation ofthe equation shown in (Equation 4) using the W-patient calculated instep S444, or the W-patient calculated in step S446, or the W-patientcorrected in step S447, displays the calculation result of the measuredentire body SAR in the SAR value display portion 840 shown in FIG. 2 asthe SAR value 842, and stores the calculation result of the measuredentire body SAR in the imaging condition storage section 606 of theinternal memory 66.

Steps S453 to S455 are a flowchart for performing the operation of(Equation 5). In step S453, in the same manner as in step S443, it ischecked whether or not the W-patient for a current target part or bedposition is stored. When the W-patient is present in the database DB2,the W-patient based on the measurement is read by search from thedatabase DB2 with the part or the bed position as a search parameter instep S454. When the W-patient is not yet present in the database DB2,W-patient of a part near the target part or W-patient of a stop positionnear the stop position of the target bed is read by search in step S456.Using the read W-patient as it is, the measured body part SAR may becalculated in step S455. In addition, it is possible to improve theaccuracy by correcting and using the W-patient of the different part orthe different bed position, which has been acquired in step S456, instep S457, instead of using the W-patient of the different part or thedifferent bed position as it is.

In step S455, the signal processing system 60 calculates the measuredbody part SAR by performing the operation of the equation shown in(Equation 5) using the W-patient calculated in step S454, or theW-patient calculated in step S456, or the W-patient corrected in stepS457, displays the calculation result in the SAR value display portion840 shown in FIG. 2 as the SAR value 842, and stores the calculationresult in the imaging condition storage section 606 of the internalmemory 66.

Steps S463 to S465 are a flowchart for performing the operation of(Equation 6). In step S463, in the same manner as in step S443, it ischecked whether or not the W-patient for a current target part or bedposition is stored. When the W-patient is present in the database DB2,the W-patient based on the measurement is read by search from thedatabase DB2 with the part or the bed position as a search parameter instep S464. When the W-patient is not present in the database DB2,W-patient of a part near the target part or W-patient of a bed positionnear as the target bed position is read by search in step S466. Usingthe read W-patient as it is, the measured head SAR may be calculated instep S465.

In addition, the W-patient of the different part or the W-patient forthe different bed position that has been acquired in step S466 iscorrected in step S467, instead of using the W-patient of the differentpart or the W-patient for the different bed position as it is. Bycorrecting the W-patient of the different part or the W-patient for thedifferent bed position as described above, it is possible to obtain themeasured head SAR value with higher accuracy than when using theW-patient of the different part or the W-patient for the different bedposition as it is.

In step S465, the signal processing system 60 calculates the measuredhead SAR by performing the operation of the equation shown in (Equation6) using the W-patient calculated in step S464, or the W-patientcalculated in step S466, or the W-patient corrected in step S467,displays the calculation result in the SAR value display portion 840shown in FIG. 2 as the SAR value 842, and stores the calculation resultin the imaging condition storage section 606 of the internal memory 66.

The flowchart shown in FIG. 10 is the details of step 314 described inFIG. 4 or step 314 described in FIG. 5, which is executed by the signalprocessing system 60. After the execution of FIG. 10, the signalprocessing system 60 executes step S316 shown in FIG. 4 or 5 todetermine whether or not each calculation result exceeds the specifiedSAR value as described above. Specific explanation is the same asdescribed above, and will be omitted. In the present embodiment, afterperforming all of the operations of (Equation 4), (Equation 5), and(Equation 6), it is determined whether or not the value of measured SARthat is the calculation result exceeds the specified SAR value in stepS316. However, whenever the operation of (Equation 4), (Equation 5), or(Equation 6) is separately completed, comparison between the value ofthe measured SAR that is the calculation result and the correspondingspecified value, which is the processing of step S316 shown in FIG. 4 or5, may be performed.

Other Embodiments Regarding the Imaging Conditions Based on MonitoringUsing the Measured SAR Value in FIG. 4

In FIG. 3, a predicted SAR value is calculated to prevent the SAR valuefrom exceeding the specified value in the actual imaging operation basedon the set imaging schedule including the imaging conditions. If asituation in which the specified value is exceeded occurs or if it ispredicted to exceed the specified value, the imaging is stopped in stepS320 in the flowchart described in FIG. 4. However, the imaging of theMRI in the target part or the bed stop position is required for theobject 1, and it is not possible to stop the imaging in many cases.Therefore, it is desirable to reset the imaging conditions appropriatelyand to resume the imaging in many cases. In this case, the operatorchanges the imaging schedule including the imaging conditions to performimaging further. An embodiment for this is shown in FIG. 11.

There is an individual difference in the energy absorption rateW-patient unique to the object 1. Accordingly, the energy absorptionrate W-patient unique to the object 1 may be greatly different from thestandard energy absorption rate W-basic for some people. By using theW-patient calculated based on the measurement value by the SARmeasurement unit 70 as described in FIG. 4, it is possible to respond tothe above case even if the individual difference is large. Therefore, itis possible to improve the calculation accuracy of the SAR value. Byperforming the SAR calculation based on the imaging conditions using theW-patient and then performing measured SAR calculation along the imagingschedule of other parts using the W-patient of the part alreadymeasured, it is possible to reduce a lowering in the accuracy of the SARdue to individual differences.

Using the W-patient for a part already measured as described above,subsequent predictive calculation of the measured SAR value along theimaging schedule can be performed to some extent. Thus, predictivecalculation of the measured SAR of other parts that have not yet beenmeasured is performed by using the W-patient already obtained bymeasurement, and it is determined whether or not the specified SAR valueis exceeded based on the calculation result (hereinafter, referred to asa predicted value of the measured SAR). When the specified SAR value isexceeded, it is desirable that the signal processing system 60 outputsthe situation through a display means or the like to prompt the operatorto change the imaging schedule including the imaging conditions. Anembodiment for this is shown in FIG. 11.

FIG. 11 is obtained by adding a new step to the flowchart described inFIG. 4. In particular, a new step is added between step S316 and stepS332 or S320. Since the other steps described in FIG. 4 areapproximately the same as already described, explanation of these stepswill be omitted.

In FIG. 11, steps S302 to S308 described in FIG. 4 are executed, andthen step S312 is executed. After step S312, step S314 is executed.Using the W-patient stored in the database DB2 that has been calculatedby the SAR measurement unit 70, the operation of the measured SAR valuebased on (Equation 4), (Equation 5), or (Equation 6) is performed instep S314. When the measured SAR value that is the calculation result isequal to or less than the specified SAR value, as in FIG. 4, the signalprocessing system 60 executes step S511 or S512 from step S316, andproceeds to step S332.

However, when there is a warning display of the warning 846 or thewarning column 848 for the scan name 152 for which the determination instep S316 has been made, the warning display of the warning 846 or thewarning column 848 is eliminated in step S511 since it has beenconfirmed that the cause of the previously issued warning is solved bythe determination in step S316. When a warning has been issued foranother scan name 152, it is necessary to perform an imaging operationafter removing the scan name 152 for which a warning has been issued byresetting the imaging conditions of the scan name 152 for which awarning has been issued.

For this reason, in step S512, it is determined whether or not there isany scan name 152 for which a warning has been issued. When there is noscan name for which a warning has been issued, the execution of thesignal processing system 60 proceeds to step S332. When there is anotherscan name for which a warning has been issued, display for asking theoperator whether to immediately change the imaging conditions of thescan name 152 for which a warning has been issued or to change theimaging conditions later is performed in step S518. Based on thedetermination of the operator, it is determined whether to execute stepS520 or to execute step S524. The details of the operation in step S511or S518 or the purpose of the operation will be described later.

On the other hand, when the measured SAR value that is a calculationresult exceeds the specified SAR value, the execution of the signalprocessing system 60 proceeds to step S516 to display the warning 846 inthe SAR value display portion 840 shown in FIG. 2 and display the scanname in the warning column 848 of the scan list display portion 810. Thedisplay of the warning 846 is a display corresponding to the selectedscan name 152. If the operator forcibly selects the next scan name inorder to check the state of warning for all of the scan names 152displayed in the list of the scan list display portion 810 or if theoperator selects to postpone responding to the warning as will bedescribed below, the execution of the signal processing system 60proceeds to processing for the new scan name.

In this case, the display of the imaging condition display portion 820is changed to the display of the state of the newly selected scan name152. As a result, the display of the warning 846 for the previous scanname 152 disappears, and the display of the warning 846 is performedaccording to the state of the new scan name 152. On the other hand, thewarning column 848 is the display of warning states for all scan namesof the list of scan names described in the scan list display portion810, and the warning display of the warning column 848 is not changedeven if the scan name 152 to be selected is changed. For example, in astate in which the measured SAR value exceeds the specified SAR value ina plurality of scan names 152, the plurality of scan names that arewarning targets are displayed in the warning column 848. Although theplurality of scan names that are warning targets are displayed in thescan list display portion 810 in the present embodiment, the warningcolumn 848 may be displayed in another location. It is very important tonotify the operator for which scan name 152 a warning has been issued.By displaying the scan name as a warning target that does not satisfythe conditions of the SAR as described above, it is possible to preventthe response error in setting the imaging conditions. Therefore, thereis a large effect in terms of the improvement in reliability or safety.

The execution of the signal processing system 60 proceeds from step S316to step S516 to display a warning in the SAR value display portion 840or the warning column 848, and proceeds from step S516 to step S518.Alternatively, when there is a scan name for which a warning has beenissued in step S512, step S518 is executed. In step S518, display forasking the operator whether to immediately respond to the cause of thewarning or to postpone the response including the stopping of theimaging is performed, and the instruction of the operator is awaited.For example, a case can be considered in which a response is determinedafter checking the presence of a warning for all of the scan namesdescribed in the scan list display portion 810. In this case, theoperator inputs an instruction of the corresponding content later.According to the instruction of the operator, the signal processingsystem 60 executes step S524. The position where there is a display forthe checking of the operator, which is performed in step S518, is notparticularly specified. However, it is easy to perform determination ifthe display is performed near the warning column 848, for example. Inaddition, various display formats can be used, and there is no need todefine a format in particular.

When the operator inputs an instruction to immediately change theimaging conditions for the display in step S518, the execution of thesignal processing system 60 proceeds from step S518 to step S520according to the instruction, and the scan name for which a warning hasbeen issued is automatically selected in step S520. In addition, thescan position 834 or the scan position 836 of the selected scan name isdisplayed in the positioning image display portion 830, and the imagingconditions including the previously set imaging parameters that causedthe warning are displayed in the imaging parameter display portion 850.In the SAR value 842 of the SAR value display portion 840, the measuredSAR value that caused the warning is displayed. In addition, thecorresponding specified SAR value 844 is displayed.

When the imaging conditions including new imaging parameters forchanging the conditions of the positioning image display portion 830 orthe imaging parameter display portion 850 are input in step S522, stepS314 is executed again. The calculation of the measured SAR value basedon the W-patient is performed by (Equation 4), (Equation 5), or(Equation 6) using the newly input information, and step S316 isexecuted again. Thus, by calculating the measured entire body SAR value,the measured body part SAR value, or the measured head SAR value using(Equation 4) to (Equation 6) described above using the W-patientobtained by the measurement and calculation of the SAR measurement unit70, it is determined whether or not the SAR conditions are satisfied. Inthis manner, the optimal imaging conditions are set.

On the other hand, when the imaging conditions for the warning are notchanged immediately, for example, when the presence of a warning is alsochecked for the imaging conditions of other scan names and then theimaging conditions are changed or the imaging operation itself isstopped in step S518, the operator inputs an instruction of “NO” for thedisplay based on step S518. According to this instruction, it isselected whether to change the imaging conditions later or to stop theimaging operation in step S518, and the execution proceeds to step S524.In step S524, display for asking about whether to simply stop theimaging operation or to check the presence of a warning for other scannames first is performed. When the operator inputs an instruction tostop the imaging, the execution proceeds to step S320 as described inFIG. 4. In step S320, the signal processing system 60 performsprocessing for stopping the imaging operation, so that the imagingcontrol is ended.

In step S524, when “imaging conditions will be changed later” isselected for purposes for determining the presence of a warning forother scan names first and the like, the execution of the signalprocessing system 60 proceeds to steps S526 and S528. In step S528, thenext scan name of the scan names 152 displayed in the scan list displayportion 810 is selected, and step S306 in FIG. 4 is executed. Therefore,it is possible to check the presence of a warning in order for all ofthe scan names 152 in the scan list display portion 810. When thepresence of a warning has been checked in order for the scan names 152in the scan list display portion 810 and the checking of all scan namesin the scan list has been completed, the completion of the checking ofall of the scan names is determined in step S526, and the execution ofthe signal processing system 60 proceeds to step S532. Display meaningthe completion of the checking of all of the scan names is performed instep S 532, and the change of the imaging conditions is started for thescan name for which a warning has been issued in step S520.

For example, considering a case in which the warning has been issued forthe first scan A 152 in the scan list displayed in the scan list displayportion 810, the execution of the signal processing system 60 proceedsfrom step S316 to step S518 through step S516. As described above, instep S516, the scan name in the warning 846 or the warning column 848 isdisplayed. When the instruction of NO is given by the operator in stepS518, step S524 is executed, and steps S526 to S528 are furtherexecuted. In step S528, a scan B 152 that is the next scan name in thescan list is selected. In the scan B, even if no warning is issued, theexecution proceeds from step S512 to step S518, step S528 is executedthrough steps S524 and S526, and a scan C 152 that is the next scan name152 is selected. When there is a warning for the selected scan name, thescan name is displayed in the warning 846 or the warning column 848 instep S316. Then, through steps S316 to S518, steps S524 to S526 areexecuted and step S528 is executed, and the selected scan names areupdated in order. Even if there is no selected scan name for which awarning has been issued, the scan names 152 selected in step S528 areupdated in order through steps S512 to S518. It is possible to check thepresence of a warning for all of the scan names 152 up to a scan E 152that is the last scan name 152. For all of the scan names 152 for whicha warning has been issued, step S516 is executed, and the relevant scannames 152 are displayed in order in the warning column 848. Therefore,results of the checking of the presence of a warning for all of the scannames are displayed in the warning column 848. The operator canunderstand the overall situation by observing the warning column 848.Thus, by understanding the overall situation, it is possible todetermine which measurement conditions are to be set. This is helpfulwhen the state of the object 1 is very different from that of thestandard person.

When the occurrence of a warning for the SAR is avoided by resetting theimaging conditions in step S520 after checking the presence of a warningfor all of the scan names 152 in the scan list displayed in the scanlist display portion 810, step S511 is executed after the determinationof “YES” in step S316, in which the scan name displayed in the warning846 or the warning column 848 is eliminated. As a result, the operatorcan check the situation of the presence of a warning due to theresetting of the imaging conditions by observing the warning column 848.

When there is a scan name for which a warning is not avoided other thanthe scan name for which a warning has been avoided by resetting theimaging conditions, the execution of the signal processing system 60proceeds to step S518 based on the determination in step S512, andproceeds from step S518 to step S520. In step S520, scan names for whicha warning has been issued are selected in order. After the selection ofthe scan name in step S520, resetting of the imaging conditions isperformed in step S522. When it is confirmed that the warning state hasbeen improved and the warning state has been avoided in step S316 basedon the calculation result in step S314, the execution proceeds from stepS316 to step S511. In step S511, scan names displayed in the warningcolumn 848 are eliminated. In this manner, when the number of scan namesfor which a warning has been issued is reduced in order and theresetting of the imaging conditions is performed for all of the scannames for which a warning has been issued so that the warning state ofall of the scan names is avoided, the execution proceeds from step S512to step S332. In step S332, the imaging operation is started. Subsequentoperation is the same as described in FIG. 4.

Even if the operator has input NO in step S518, the execution proceedsfrom step S524 to step S526 and to step S532. In step S532, displayshowing that determination regarding the presence of a warning has beenmade for all of the scan names is performed, and step S520 is executed.However, when the operator wants to stop the imaging operation, theexecution proceeds from step S524 to step S320 to stop the imagingoperation.

Even if there is a possibility that the measured SAR value will exceedthe specified value since the state of the object 1 to be imaged isgreatly different from the W-basic that is standard data shown in FIG.7, it is possible to quickly respond to this situation through theoperation shown in FIG. 11.

Relationship Between a Standard Bed Position and a Bed Position Uniqueto the Object 1

In the present embodiment, a part that is an object to be imaged and abed position are used as search parameters in the database DB1 or thedatabase DB2 shown in FIG. 7 or 8. Also in the column of the imagingparameter display portion 850 described in FIG. 2, there is an inputcolumn and a display column of the bed position, so that the bedposition 856 is displayed. The bed position that is input or displayedin this column is used for position control for the imaging of theobject 1. The bed position shown in FIG. 7 or 8 and the bed positionthat is input or displayed in the imaging parameter display portion 850may be a bed position for a standard person, or may be a bed positioncorresponding to the individual object 1.

However, it takes time to specifically measure the position of each partcorresponding to each object 1, and this is not so efficient. Inaddition, as search parameters of the database DB1 or the database DB2,search parameters that can be normally used for a lot of people areconvenient in terms of many points. For this reason, the bed position istreated in the dimensional relationship with respect to the standardperson. In addition, when the signal processing system 60 actually movesthe top plate 84 of the bed 82 through the bed control device 80 or andperforms the specific control, the bed position for the standard personis used after being converted into a bed position corresponding to theindividual object 1 using the data obtained from the height, weight andthe scanogram described in FIG. 3, which are the input personal data ofthe object 1. Instead of the data of the bed position for the standardperson, personal data obtained by measuring the position of a part ofthe individual object 1 may be also be used for input and display.Alternatively, both the standard bed position data and the individualbed position data may be used, so that the operator can use these piecesof data selectively.

Embodiment in Which W-patient is Used Instead of W-basic

The embodiment for setting the imaging conditions satisfying thespecified SAR value based on the predicted SAR value using the W-basic,which is the data of the standard SAR absorption rate, has beendescribed previously with reference to the flowchart described in FIG.3. However, instead of the W-basic that is the data of the standard SARabsorption rate, W-patient that is the personal SAR absorption rate of aperson for whom imaging is scheduled.

An embodiment in which the imaging conditions satisfying the specifiedSAR value are set by calculating the measured SAR using the W-patientthat is the personal SAR absorption rate of a person for whom imaging isscheduled will be described with reference to FIG. 12.

In the embodiment shown in FIG. 3, it is determined whether or not theset imaging conditions satisfy the specified SAR value by calculatingthe predicted SAR value using the W-basic, which is a standard SARabsorption rate, and comparing the predicted SAR value with thespecified SAR value. There is an individual difference for whether ornot the W-basic that is a standard SAR absorption rate and the W-patientthat is the SAR absorption rate for the individual object 1 for whomimaging is scheduled are close values. Depending on a person, thedifference may be large. The embodiment described in FIG. 12 is anembodiment in which the operations of (Equation 4), (Equation 5), and(Equation 6) are performed using the personal W-patient of the object 1calculated by the SAR measurement unit 70 and it is determined whetheror not the set imaging conditions satisfy the specified SAR value. Stepsfor approximately the same operations as in FIG. 3 are denoted by thesame reference numerals, and repeated explanation will be avoided ifpossible.

When the signal processing system 60 starts the execution of theflowchart shown in FIG. 12, an examination part of the object 1 or thebed position, name, weight, height, age, and the like corresponding tothe part are input based on an input image displayed by the signalprocessing system 60 in step S102. The signal processing system 60assigns the scan name 152 in order corresponding to the input part orbed position, and displays the scan name 152 in the scan list displayportion 810. In step S104, the object 1 is placed on the top plate 84 ofthe bed 82. For example, the top plate 84 is controlled, based on thesignal of the marker 15, so that the reference position of the object 1comes to the center position of the gradient magnetic field in thegantry. Therefore, it is possible to control the bed 82 according to apart or bed position data L1 to L13 so that each part of the object 1comes to a predetermined position in the gantry. Instead of the input ofa part to be imaged in step S102, it is also possible to input a bedposition for specifying a part. In addition, both a part to be imagedand a bed position for specifying the scan position may be input. Inthis case, based on the information of the input part and the input bedposition, the top plate 84 of the bed 82 is controlled through the bedcontrol device 80.

Although the explanation of step S562 or step S566 in FIG. 12 is omittedin the explanation of FIG. 3, it is also possible to perform anoperation described below in FIG. 3. In step S562, when a plurality ofparts or bed positions have been previously input in step S102, one ofthe plurality of input parts or bed positions is selected, for example,in the order of the display of the scan list display portion 810. Forexample, the first scan A is specified among the scan names of the scansA to E displayed in the scan list display portion 810, and the head thatis a part to be imaged of the scan A is selected. In addition, thesignal processing system 60 controls the top plate 84 of the bed 82through the bed control device 80 so that the object 1 is disposed at aposition where the scanogram of the head is to be captured.

In step S106, a scanogram is captured by emitting RF pulses from theirradiation coil 48. In step S564, the SAR measurement unit 70 measuresthe W-patient that is the actual SAR absorption rate of the object 1.The W-patient obtained by the measurement indicates the personal SARabsorption rate of the object 1. The signal processing system 60 storesthe calculated W-patient in the internal memory 66 as data of thedatabase DB2. In this case, the search parameter for searching thedatabase DB2 is a part or a bed position or both. Needless to say, inorder to select the database DB2 corresponding to the individual object1 from among a number of databases DB2, data specifying the object 1,for example, the name or the specific number is used. For example, inthe present embodiment, it is possible to specify the database DB2corresponding to the object 1 from a plurality of stored databases usingthe name and to search for and read the W-patient, which is previouslystored, from the specified database DB2 with a part or the bed positionas a search parameter.

It is preferable that the SAR measurement unit 70 calculates theW-patient based on the irradiation of RF pulses in the actual imagingstate. On the other hand, the output of RF pulses required to capturethe scanogram is smaller than the output of RF pulses in the actualimaging state. However, using the irradiation of RF pulses for capturingthe scanogram, it is possible to check the state of the individualdifference, which causes a difference between the W-basic that is astandard SAR absorption rate and the W-patient that is the SARabsorption rate of the individual object 1, due to calculating theW-patient. Therefore, it is possible to reduce the error based on theindividual difference by using the W-patient obtained using the RFpulses for capturing the scanogram. In addition, since there is data ofboth the W-basic that is a standard SAR absorption rate and theW-patient that is the SAR absorption rate of the individual object 1,the value of the W-patient obtained using the RF pulses for capturingthe scanogram may be corrected and used when necessary.

When there is one part or one bed position to be imaged, the signalprocessing system 60 determines that the capturing of the scanogram orthe detection of the W-patient has ended in step S566, and the executionof the signal processing system 60 proceeds to the next step S112. Whena plurality of parts or a plurality of bed positions to be imaged arepresent, it is determined that parts or bed positions to be processedare present in step S566, and the execution of the signal processingsystem 60 proceeds to step S562 again. Then, the above-describedoperation is repeated. In this manner, for all of the input parts or bedpositions, the W-patient is measured by the SAR measurement unit 70. Thevalue of the W-patient that the signal processing system 60 acquiresfrom the SAR measurement unit 70 is stored with the part or the bedposition as a search parameter as shown in FIG. 8, and is stored as thedatabase DB2 in the internal memory 66. In FIG. 8, the head to the feetare described as imaging parts. In the present embodiment, however, theSAR measurement unit 70 measures the W-patient for the part or the bedposition input in step S102, and the database DB2 is created from theW-patient measured by the SAR measurement unit 70.

In order to input and set the imaging conditions, a scan list is readout to the scan list display portion 810 described in FIG. 2 in stepS112, and the scan name 152 in the scan list is selected in step S114.The selection is performed in display order, for example. In step S116,a scanogram relevant to the selected scan name 152 is read, and isdisplayed in the positioning image display portion 831. As describedabove, based on the display in the image display portion 831, it ispossible to input the scan position 834 or the scan position 836. Instep S564, the scan position 834 or the scan position 836 is input andset, and the imaging parameters are input and set. In FIG. 12, theoperations of S 122 or step 124 and step S132 in FIG. 3 are collectivelydescribed as step S564.

When the imaging conditions including the scan position or the imagingparameter of the scan name selected in step S114 are roughly input instep S564, processing for checking whether or not the condition that theSAR value does not exceed the specified SAR value is satisfied in thecase of imaging under the input imaging conditions is performed in stepsS572, S574, and S136 for the confirmation of the safety regarding theSAR. First, in step S572, the W-patient that is the data of the databaseDB2 that the signal processing system 60 has acquired from the SARmeasurement unit 70 and stores in previous step S564 is read with thepart or the bed position as a search parameter. In step S574, themeasured entire body SAR, the measured part SAR, or the measured headSAR is calculated based on (Equation 4), (Equation 5), or (Equation 6)using the W-patient that is the read data. In step S574, the calculationresult is displayed as the SAR value 842 in the SAR value displayportion 840 of the imaging condition display portion 820 described inFIG. 2, and the specified SAR value 844 is further displayed.

In step S136, it is determined whether or not the measured entire bodySAR, the measured part SAR, or the measured head SAR calculated based on(Equation 4), (Equation 5), or (Equation 6) described above is a valuesmaller than the specified SAR value set for each of them. When any ofthe three kinds of SAR values calculated as described above exceeds thespecified SAR value set for each of them, “NO” is determined in stepS136 and a warning is displayed in the SAR value display portion 840 orthe warning column 848 in step S138. The operation in step S136 isapproximately the same as step S136 described in FIG. 3 or step S316described in FIG. 4.

After displaying the warning in the SAR value display portion 840 or thewarning column 848 in step S138, the process returns to step S564 tore-input the imaging conditions including the scan position and theimaging parameter in order to lower the value of the SAR that is thecause of the warning. On the other hand, when it is determined that allof the operation values calculated based on (Equation 4), (Equation 5),or (Equation 6) do not exceed the corresponding specified SAR values instep S136, the execution proceeds from step S136 to step S139, and therelevant warning is eliminated when the warning has been issued in theSAR value display portion 840 or the warning column 848 in step S138.Then, in step S140, it is determined whether or not the input andsetting of the imaging conditions have been completed for all of thescan names 152 displayed in the scan list display portion 810. When theinput and setting of the imaging conditions have not been completed, theexecution proceeds to step S114 in which the next described scan name152 is selected, the above-described operation is repeated, and theimaging conditions are determined The above operation is repeated untilthe input and setting of the imaging conditions for all of the scannames 152 are completed. When the setting of the imaging conditions hasbeen completed, it is determined that the setting of the imagingconditions has been completed for all of the scan names 152 in stepS140, and imaging steps are executed. The imaging operation is performedbased on the set imaging conditions, and specific explanation thereofwill be omitted.

Embodiment of the Setting of Imaging Schedule Considering the ImagingTime

In the embodiment described above, it has been determined whether or notthe specified value of the SAR is exceeded separately for each scan name152 that is input and displayed in the scan list display portion 810. Anembodiment described in FIG. 13 relates to a method of setting theimaging conditions satisfying the specified value of the SAR by changinga plurality of imaging operations, that is, a scan schedule. Needless tosay, both the method described in FIG. 13 and the method describedpreviously may be used together. The “concept of changing the scheduleof imaging operation” used herein includes not only the concept ofchanging the order of imaging for scan names for which imaging isscheduled but also the concept of changing the moving speed of the bed82 or the concept of changing the time until the RF pulses for imagingare emitted after the movement of the bed 82 is stopped.

In step S602 shown in FIG. 13, it is determined whether or not thespecified value of the SAR is exceeded for each scan name 152 describedin the scan list display portion 810. The procedure up to step S602 isthe same as described in the previous embodiment. For example, step S602includes an operation corresponding to step S316 or step S512 describedin FIG. 11.

The basic idea of the response to the determination result in step S602is that, when all of the scan names for which imaging is scheduledsatisfy the conditions of the SAR, the imaging operation may be startedas it is, but it is possible to change the setting of the imagingconditions, such as shortening the imaging time or increasing the outputof RF pulses. On the other hand, when one or more scan names for whichthe conditions of the SAR are not satisfied are present in all of thescan names for which imaging is scheduled, the imaging conditions of therelevant scan name may be changed instead of responding to the case bychanging only the imaging conditions of the scan name that does not meetthe criteria. However, there is another method in which the timerequired for imaging is increased or the waiting time is set orincreased so that the conditions of the SAR are also satisfied for thescan name for which the conditions of the SAR are not satisfied.

In step S602, it is determined whether the prediction state is that allof the scan names 152 described in the scan list display portion 810 isless than the specified value of the SAR and the conditions of the SARare satisfied or that the conditions of the SAR are not satisfied on thecontrary. First, it is assumed that all of the scan names 152 describedin the scan list display portion 810 are less than the specified valueof the SAR and accordingly it can be determined that the conditions ofthe SAR are satisfied. In step S622, if there is a warning that has beenissued before, specifically, a warning in the warning column 848 or thewarning 846, the warning is eliminated.

Then, in step S624, since the imaging operation can be started in thisstate, it is determined whether or not to start the imaging with theimaging conditions and imaging schedule in this state. Specifically,display for asking the operator about the determination is performed.When the operator determines that the imaging is to be started withoutfurther adjusting the imaging schedule or the like, the execution of thesignal processing system 60 proceeds from step S624 to step S626according to the operation instruction from the operator, and theimaging operation is started. Then, when the imaging ends, processingfor the end of the imaging is performed in step S630. For example, whenthe operator selects the imaging start mark 860 described in FIG. 2, theexecution of the signal processing system 60 proceeds from step S624 tostep S626 to start the imaging operation.

As described above, even if the conditions of the SAR are satisfied, itis possible to increase the output of RF pulses by shortening the timerequired for imaging or by changing the imaging conditions. Thus, it ispossible to further improve the workability or to further improve thequality of imaging. In this case, based on the operation of theoperator, the execution of the signal processing system 60 proceeds fromstep S624 to step S614, and the imaging conditions or the imagingschedule is changed in step S634 or step S638. In step S614, it isdetermined whether the operator himself or herself changes the imagingconditions or the imaging schedule or the signal processing system 60automatically makes a change proposal. When display for asking theoperator is performed and the signal processing system 60 makes a changeproposal automatically in step S614, the execution of the signalprocessing system 60 proceeds from step S614 to step S638 according tothe operation instruction from the operator.

In step S638, the signal processing system 60 changes the order of thescan name list automatically, thereby changing the imaging order. Thewaiting time is changed according to the change of the imaging order.Alternatively, only the waiting time may be changed without changing theimaging order. The signal processing system 60 changes the waiting timeor changes the imaging order so that the conditions of the SAR aresatisfied. A new change result is displayed on the scan order candidatedisplay portion 880 shown in FIG. 2. Here, the content displayed in thescan order candidate display portion 880 is approximately the same asthe content displayed in the imaging schedule display portion 870 to bedescribed below. A large difference between the content displayed in theimaging schedule display portion 870 and the content displayed in thescan order candidate display portion 880 is that the display content ofthe imaging schedule display portion 870 is input by the operatorhimself or herself in step S634 to be described below and the displaycontent of the scan order candidate display portion 880 is automaticallycalculated by the signal processing system 60 in step S638.

The calculation of the imaging time, the moving speed of the bed, andthe waiting time and the total calculation according to the processingof step S638 is performed in step S639, and the result is additionallydisplayed in the display content of the scan order candidate displayportion 880. As described above, the display shown in FIG. 14 is adisplay of the imaging schedule display portion 870, but is basicallythe same as the display content of the scan order candidate displayportion 880. The same content as the content obtained by the calculationin step S639 is added to the content in FIG. 14, and the display contentof the scan order candidate display portion 880 in step S639 is the sameas the content shown in FIG. 14. In step S640, the operator determineswhether or not to start the imaging operation according to the displayof the scan order candidate display portion 880 described above. Theoperator determines whether or not to start the imaging operation basedon the display content of the scan order candidate display portion 880.When the operator starts the imaging operation, the execution of thesignal processing system 60 proceeds from step S640 to step S626according to the instruction from the operator, thereby starting theimaging operation. On the other hand, when it is necessary to change theimaging schedule or the like, the execution proceeds from step S640 tostep S634 according to the instruction from the operator.

When there is a scan name that does not meet the SAR criteria in stepS602, a warning is displayed in the warning 846 or the warning column848 in step S612 of the signal processing system 60, and the executionof the signal processing system 60 proceeds to step S614. In step S614,as described above, it is determined whether the signal processingsystem 60 automatically responds to the situation or the operatorhimself or herself responds to the situation. When the operator himselfor herself makes an instruction to change the imaging schedule or thelike in step S614, the execution of the signal processing system 60proceeds from step S614 to step S634. When the operator himself orherself inputs the imaging schedule or the like without accepting thechange proposal obtained by the calculation of the signal processingsystem 60 in step S640, step S634 is executed after step S640 even ifthe instruction is given.

The processing of step S634 will be described with reference to FIG. 14.In step S634, not only the imaging schedule but also the imagingconditions may be changed instead of changing only the imaging schedule,or only the imaging conditions may be changed without changing theimaging schedule. The change of the imaging conditions is the same asdescribed in the above embodiment. In the present embodiment, the changeof the imaging schedule will be described.

Specifically, the change of the imaging schedule is to change theimaging order of the scan name 152 described in the scan list displayportion 810 or to increase the waiting time. Although the waiting timeis changed by changing the imaging order in many cases, only the waitingtime may be changed without changing the imaging order. Here, theprocessing for the change of the waiting time includes processing forthe change of the moving speed of the top plate 84 of the bed 82.

FIG. 14 shows the display content of the imaging schedule displayportion 870 when the imaging order of the scan name has been changed.For example, the imaging schedule display portion 870 is provided in thesetting image 800 in FIG. 2, and information regarding the order,waiting time, and the like according to the execution of the imagingschedule is displayed. An item 652 indicates an imaging order, and anitem 654 indicates a scan name for which imaging is scheduled. In thepresent embodiment, the imaging operation of each scan name is performedaccording to the order described in the item 654. The order of the scanname in the item 654 is the same as the order of the scan name 152 inthe scan list display portion 810 described in FIG. 2, and it ispossible to change the order of imaging by changing the order of thescan name 152 in the scan list display portion 810 or by changing theorder of the scan name in the item 654 in FIG. 14. When the order of thescan name is changed in one of the scan list display portion 810 and theitem 654, the order of the scan name in the other one is automaticallychanged accordingly.

An item 656 indicates a part of an imaging target, and an item 658indicates a bed position, that is, a stop position of the top plate 84of the bed 82 for imaging. In the example shown in FIG. 14, the partdescribed in the item 656 and the bed position described in the item 658correspond to each other in a one-to-one manner. However, as shown inFIG. 7 or 8, since each part has a wide range, it is possible to set aplurality of bed positions for one part in order to control the imagingposition in each part in more detail. In this case, a scan name isassigned to each bed position. The calculation result of the SARcalculated in step S636 is displayed. As the displayed calculation valueof the SAR, there is a case of a predictive calculation resultcalculated based on (Equation 1) to (Equation 3), and there is also acase of a measurement calculation result calculated based on (Equation4) to (Equation 6). Although there are three kinds of calculationresults of the SAR for each scan name in practice, only one is describedby omitting the others. In addition, a value shown as the specified SARvalue is a specified value of the SAR that should not be exceeded.Although there are three kinds of specified values of the SAR for eachscan name in practice, they are omitted.

An item 662 is a time required for the imaging operation set for eachscan name, and is a time for which RF pulses are emitted from theirradiation coil 48. An item 664 is a time for which no imaging isperformed including the moving time of the top plate 84 of the bed 82,that is, a time for which no RF pulse is emitted. The sum column of theitem 662 or the item 664 is the time of the sum of each item.

An item 666 is the moving speed of the top plate 84 of the bed 82. Inaddition, the sum column is the sum of the movement time of the topplate 84 of the bed 82. A setting display 872 is a display fordetermining the input or change result in FIG. 14. When the settingdisplay 872 is selected, the content described in FIG. 14 is set anddetermined.

As an example for explanation, explanation will be given on theassumption that the description order of the scan name described in theitem 654 in FIG. 14 or in the scan list display portion 810 in FIG. 2 isthe order of scan A, scan B, and scan C initially and the order of thescan B and the scan C is changed in step S634 in FIG. 13. FIG. 14 showsa state in which the order of the scan B and the scan C has been changedwith the cursor 150. When the head is located at the center of thegradient magnetic field first, imaging is started from the head, and iscontinued in order along the movement of the bed 82 in a direction fromthe head to the feet. In this manner, the movement time of the bed 82 isshort, and the time required for imaging is short. In FIG. 14, if theimaging of the abdomen of the scan C is performed after the imaging ofthe head of the scan A and then the imaging of the chest of the scan Bis performed, the movement direction of the top plate 84 of the bed 82is changed. As a result, the movement overlaps the former movement. Forthis reason, if the order of the imaging of the scan B and the scan C ischanged, the waiting time according to the movement of the bed 82 isincreased. However, by increasing the waiting time, it is possible toreduce the value of the SAR that is the amount of absorption of theenergy of RF pulses per unit time.

For the above reasons, if the operator changes the description order ofthe scan name in the item 654 in FIG. 14, the imaging order is changedbased on the operation of the operator, and the movement time of the bed82 according to the change is automatically calculated. The waiting timeobtained by the calculation is displayed in the item 664. The exampleshown in FIG. 14 is an example of increasing the waiting time forreducing the value of the SAR, which is the amount of absorption of theenergy of RF pulses per unit time, by changing the imaging order. Inorder to reduce the value of the SAR that is the amount of absorption ofthe energy of RF pulses per unit time, it is important to increase thewaiting time, and it is also possible to change the waiting time of theitem 664 without changing the imaging order. In this case, for example,the waiting time of the relevant scan name in the item 664 is designatedwith the cursor 150, and input for increasing the waiting time isperformed. If the waiting time is increased, the top plate 84 of the bed82 is controlled so as to move slowly according to the waiting time, forexample. As another example, no RF pulses may be emitted from theirradiation coil 48 until the waiting time elapses even if the movementof the top plate 84 of the bed 82 ends.

The above explanation is relevant to the operation for reducing thevalue of the SAR that is the amount of absorption of the energy of RFpulses per unit time, and is a method of reducing the value of the SARthat is the amount of absorption of the energy of RF pulses byincreasing the waiting time of the scan B or the scan C in the item 664.On the other hand, when the conditions of the SAR are satisfied in stepS602, processing for reducing the time required for the imaging of theobject 1 by reducing the waiting time on the contrary is performed instep S364. In this case, the value of the waiting time is changed in adecreasing direction. Thus, through the processing in step S634, thewaiting time of the item 664 is changed in an increasing direction or ina decreasing direction. In step S635, based on the newly changed imagingschedule, the total time of the item 662 or the item 664 or the movingspeed of the bed 82 or the sum of movement time of the item 666 iscalculated.

In step S634, the waiting time of the item 664 is increased or decreasedas described above. Reducing the time until the imaging is started afterthe movement of the bed 82 leads to the improvement of the work. In somecases, if the time until the imaging is started after the movement ofthe bed 82 is stopped is long, object 1 may feel uneasy. Therefore, itis preferable to control the moving speed of the top plate of the bed82, which is the moving speed of the bed 82, according to the waitingtime.

$\begin{matrix}{{{Bed}\mspace{14mu} {moving}\mspace{14mu} {speed}\mspace{14mu} {SB}\; \left( {{mm}\text{/}s} \right)} = {\frac{D({mm})}{{{Tw}(s)} - \frac{D({mm})}{S\; 0\left( {{mm}\text{/}s} \right)}} + {So}}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

Here, Tw≠D/So. Here, BS (mm/S) is the moving speed of the top plate 84of the bed 82, Tw (s) is a waiting time, D (mm) is a moving distance,and So (mm/s) is the initial moving speed of the top plate 84. Byadjusting the moving speed of the bed based on (Equation 7), it ispossible to gently move the object 1 using an increase in the waitingtime when the waiting time is increased. Therefore, it is possible toreduce the physical impact of the object 1. In addition, since anincrease in the time interval up to the imaging operation after themovement of the bed is stopped can be suppressed, it is possible toreduce the psychological pressure on the object 1. In addition, sincethe moving speed of the top plate 84 of the bed 82 can be increasedwithin the range satisfying the SAR conditions, the efficiency of theimaging operation is improved. In addition, since it is possible toshorten the total time required for the imaging of the object 1, it ispossible to reduce the burden on the object 1 from the overall point ofview.

When the waiting time is changed by changing the imaging order or thewaiting time of imaging is changed as described above in step S634 shownin FIG. 13, the calculation of the SAR value based on the new conditionsis performed in step S636. In step S602, it is determined whether or notthe calculated SAR value satisfies the conditions of the SAR. Unlike theembodiment described above, according to the embodiment shown in FIG.13, it is possible to use the waiting time as a method satisfying theconditions of the SAR. Since the number of solutions for satisfying theconditions of the SAR is increased, a wide range of response includingthe method described in the above embodiment becomes possible.

FIG. 15 shows standard data indicating the relationship between a partand height in the database DB1 shown in FIG. 7 or the database DB2 shownin FIG. 8, and the standard data is stored in the internal memory 66.FIG. 15 shows data in which a toe portion is a reference, the toeportion is disposed at the center of the gradient magnetic field, andthe head is located farthest from the center of the gradient magneticfield (hereinafter, referred to as feet first). On the contrary, fromthis data, data in which the parietal is a reference, the head isdisposed at the center of the gradient magnetic field, and the feet arelocated farthest from the center of the gradient magnetic field(hereinafter, referred to as head first) can be easily obtained bycalculation. Using the part data of the standard person shown in FIG.15, conversion into the information of the unique part position of theobject 1 to be imaged can be performed when necessary using the heightinformation of the object 1. For the database DB1 or the database DB2shown in FIG. 7 or FIG. 8, it is desirable to use the relationshipbetween a part and a bed position or to use the value of the bedposition for the standard person in the search process of W-basic, headabsorption rate, or W-patient using bed position as a search parameter.Therefore, databases including the database DB1 or the database DB2 arecreated based on the height or physique of the standard person shown inFIG. 15. On the other hand, when using the data retrieved from thesedatabases, the bed position based on the standard person is used afterbeing converted into the value of the individual object 1.

FIG. 16 is a flowchart for converting the position of an input part ofthe object 1, in which imaging is scheduled, into the moving length ofthe top plate 84 of the bed 82 or for setting the relationship between aposition where the object 1 is placed and the gradient magnetic fieldcenter, which is the reference position of the gantry, or therelationship between the position where the object 1 is placed and thereference position of the top plate 84 of the bed 82. In step S710, animaging scheduled part or personal information of the object 1 is input.As the imaging scheduled part of the object 1, a plurality of parts canbe input at a time. For example, as shown in FIG. 2, a scan name isassigned to each of the input parts. Although the imaging scheduled partis input in step S710 in this example, a distance from the referencepoint in the standard person shown in FIG. 15 or the movement stopposition of the top plate 84 may be input for the imaging positioninstead of a part. In order to input the stop position of the top plate84 with the individual value of the object 1 that is a person for whomimaging is scheduled, it is necessary to measure the length from thereference point of the imaging position of the object 1 one by one. Thisis very troublesome. As shown in FIG. 15, it is efficient to input thevalue based on the standard positional relationship. This is alsoconvenient for data search or the like.

In step S712, the object 1 is placed on the top plate 84 of the bed 82.As a direction in which the object 1 is placed, for example, there is ahead first direction in which the head moves to the center of the gantryfirst as described in FIG. 17 or a feet first direction in which thefeet move to the center of the gantry first as described in FIG. 18. Instep S712, a marker is attached to the reference position and the partof the object 1. In this case, it is not necessary to attach a marker toall parts to be imaged, and a marker may be attached to one or twoplaces. Then, in step S714, it is input whether the object 1 has beenplaced in the head first direction with respect to the top plate 84 orplaced in the feet first direction. This information is used tocalculate the relationship between the input part and the bed position.

In the mounting example described in FIG. 17, a reference marker 262used as a reference is fixed to the head of the object 1, and a partmarker 272 is fixed to the abdomen that is an imaging scheduled part.Not only the part at the position of the part marker 272 but also thepart at the fixing position of the reference marker 262 can be imaged.The specification of the positions of other parts to which no marker isattached is also possible from the positional relationship of thereference marker 262 or the part marker 272, and it is possible toperform imaging by stopping the movement of the top plate 84 at theposition of the input part.

One method of determining the position of an imaging scheduled part ofthe object 1 by calculation is a method of measuring the length of thereference marker 262 and the part marker 272 unique to the object 1 fromthe positional relationship of the reference marker 262 and the partmarker 272 and calculating a distance from the reference position of theimaging scheduled part unique to the object 1 by performing aproportional operation based on the difference in the length withrespect to the standard database described in FIG. 15. Another method isa method of calculating the distance between the imaging schedule partof the object 1 and the reference marker 262 by calculating the ratiobetween the input height of the object 1 and the height of the standarddata in FIG. 15 and converting the standard distance from the referenceposition for each input part into the distance unique to the object 1.In the mounting method in FIG. 17, it is possible to stop the top plateat the calculated distance of the imaging scheduled part with thereference marker 262 as a reference point.

In the example shown in FIG. 18, the reference marker 262 used as areference is fixed to the feet of the object 1, and the part marker 272is fixed to the abdomen that is an imaging scheduled part. Also in thisexample, as described above, by detecting the distance between thereference marker 262 and the part marker 272, it is possible tocalculate the personal value of the input position of the imagingscheduled part based on the data in FIG. 15. Therefore, it is possibleto control the movement or stop of the top plate 84 based on thepersonal value of the object 1. In addition, as described above, byusing the reference marker 262 and the data of the height of the object1, it is possible to perform the same operation and control even if thepart marker 272 is not used.

In FIG. 17 or 18, a movement direction 252 indicates a movementdirection of the top plate 84. When the top plate 84 moves in step S716,the reference marker 262 is first moved to the center position of thegradient magnetic field that is a gantry center. In step S718, thereference marker 262 is detected, and the relationship between thereference position of the top plate 84 and the reference marker 262 isstored. In step S720, the top plate 84 is moved, and the part marker 272is detected. The positional relationship between the part marker 272 andthe reference position of the top plate 84 or the distance informationbetween the reference marker 262 and the part marker 272 is measured andstored.

Then, in step S722, other imaging scheduled parts that have been inputare read. In step S724, the distance between each of the read parts andthe reference marker 262 or the distance of the top plate 84 from thereference position is calculated by operation, and the calculated valueis stored. After step S724, processing required for imaging, such asstep S726 in the embodiment that has been previously described, isperformed.

FIG. 19 is a flowchart for inputting an imaging scheduled part, and FIG.20 is an image displayed on the display 18 provided in gantry. The imageshown in FIG. 20 is not limited to being displayed on the display 18provided in the gantry, and may be displayed on a display 98 or may bedisplayed on both the displays 18 provided in the gantry and the display98.

In addition, the display 18 provided in the gantry shown in FIG. 20includes a touch panel or the like. Therefore, not only the display butalso the input or cancellation of an imaging scheduled part based on thetouching of a displayed image can be performed.

The image displayed on the display 18 provided in the gantry includes amodel image 182, a part input image 186, a relationship display 184showing the relationship between the model image 182 and the part inputimage 186. In the part input image 186, a part name 188 as an imagingtarget is displayed. For example, when the head of the part name 188 isselected by an operation, such as a touch, the head that is the selectedpart name and the head of the model image 182 are connected to eachother through the relationship display 184. Therefore, it can be seenthat the head has been input as an imaging scheduled part. In the aboveexplanation, an imaging scheduled part is input by designating the partinput image 186. However, when an imaging scheduled part is designatedfor the image of the model image 182, for example, when the head of themodel image 182 is touched, the head is input as an imaging scheduledpart, and the relationship display 184 is displayed. When the part thathas been input is selected again by a touch operation or the like in themodel image 182 or the part input image 186, the previous input state isreset, and the relationship display 184 of the target that has beendisplayed is eliminated. When the imaging scheduled parts are input inorder, scan names are assigned in the input order, and are displayed inthe scan list display portion 810 in FIG. 2.

FIG. 21 is a diagram for explaining an input portion 190 provided in thetop plate 84. Through the input portion 190, it is possible to input orcancel an imaging scheduled part. The input portion 190 has an inputfunction. In addition, an operation button 192 that is an example of anoperation means is provided in the input portion 190 corresponding toeach part name 194. The color of the operation button 192 that is anexample of the operation means is changed in the input state.Accordingly, the input portion 190 also has a function of displaying aninput state or a non-input state. When the part names 194 displayed inthe input portion 190 are selected in order according to the imagingschedule, the part names are input in order. For example, in order toimage the head of the object 1 placed on the top plate 84, when theoperation button 192 that is an operation means corresponding to thepart name 194 is selected, the color of the operation button 192 ischanged and it is displayed that the part of the head has been selected.When a plurality of part names 194 are selected, the colors of theplurality of operation buttons 192 corresponding to the selected partnames 194 are changed. Therefore, it can be seen that a plurality ofpart names have been input.

When both of the input portion 190 shown in FIG. 21 and the part inputimage 186 or the model image 182 described in FIG. 20 are used, thedisplay state of the operation button 192 of the relevant part name 194in the input portion 190 is changed to the display of the input statebased on the input from the display 18 provided in the gantry. On thecontrary, for the input from the input portion 190, the display statebecomes a display state showing that the input has been performed in thedisplay 18 provided in the gantry. That is, the relationship display 184is displayed so that the relationship between the input part name 188and the model image 182 can be seen. It is possible to perform aresetting operation for returning the part name 188 or the part name194, which has already been input, to the state in which there is noinput from the display 18 provided in the gantry or the input portion190. Even before the object 1 described in FIG. 21 is placed on the topplate 84 or even after the object 1 described in FIG. 21 is placed onthe top plate 84, the input from the input portion 190 is possible.

In addition to the input or display of the imaging scheduled part fromthe display 18 provided in the gantry that is shown in FIG. 20, theinput or display of the imaging scheduled part is also possible in theinput portion 190 shown in FIG. 21. The display 18 provided in thegantry that is shown in FIG. 20 or the input portion 190 shown in FIG.21 is an example of the input or display of the imaging scheduled part,and both of the display 18 and the input portion 190 may be provided orone of them may be provided. Although it is very convenient if they areprovided, the function of the input or display of the imaging scheduledpart is not essential since the input and output device 90 also has thefunction.

FIG. 19 is a flowchart for inputting a part to be imaged. When theexecution of the flowchart is started in step S740, the model image 182or the part input image 186 is displayed on the display 18 provided inthe gantry in step S742, so that a part can be input on the display 18provided in the gantry. In addition, an input from the input portion 190is also possible. The top plate 84 is located in a place where it iseasily touched by a person. For this reason, if an input through theinput portion 190 is made possible at all times, there is a concern thaterroneous input will occur in a state in which the object 1 is placed.Therefore, the erroneous input can be prevented by permitting an inputoperation as in step S742 or the like.

In step S744, it is checked whether or not there has been an input. Whenthere is an input of a part, step S745 is executed. In step S745, it isdetected whether the input part is a new input or a part that hasalready been input and accordingly an operation of canceling the input.In the present embodiment, input cancel is determined when the inputoperation is performed again for the state in which there has alreadybeen an input. For the first input part, in step S746, the input part isstored. In step S748, the relationship display 184 is displayed on thedisplay 18 provided in the gantry that is described in FIG. 20, and thecolor of the corresponding operation button 192 of the input portion 190shown in FIG. 21 is changed. A scan name is assigned to the input part,and the scan name is displayed in the scan list display portion 810shown in FIG. 2.

On the other hand, when it is determined that re-input has beenperformed for a part that was already input in step S745, step S747 isexecuted to eliminate the information of the input part from the storagedevice. Then, in step S749, the display 184 shown in FIG. 20, which hasbeen displayed on the display 18 provided in the gantry and a means thatan input has been completed, is eliminated. In addition, in the inputportion 190 shown in FIG. 21, a display showing that this is the inputstate of the relevant part is changed to a display showing that this isa no-input state. In addition, the relevant scan name displayed in thescan list display portion 810 in FIG. 2 is eliminated.

When no input operation has been performed in step S744, the executionproceeds from step S744 to step S750 to determine whether or not this isa state meaning the end of the part input operation. For example, whenan operation meaning the end of the input operation has been performed,it is determined that the input of a part has ended, and the nextprocessing for imaging is performed in step S754. In the case of a statein which a part input operation has not ended, the execution returns tostep S744 to determine whether or not the input of a part has beenperformed.

By inputting a part using the method described in FIG. 19, 20, or 21, itis possible to input a part in a very simple way. For the input part, ascan name is assigned for each input as a part to be imaged. Inaddition, the input part is displayed in the scan list display portion810 in FIG. 2, and the imaging conditions are set for each scan name asdescribed above. By searching for the database DB1 of the W-basic or thedatabase DB2 of the W-patient based on the part input as describedabove, it is possible to calculate the SAR using the data of the W-basicor the data of the W-patient that corresponds to the part. Therefore, itis possible to calculate the predicted SAR value or the measured SARvalue with high accuracy. This leads to the setting of the correctedimaging conditions.

REFERENCE SIGNS LIST

1: object

12: sequencer

14: central processing unit (CPU)

15: marker

18: display provided in the gantry

20: static magnetic field generating source

30: magnetic field generating system

32: gradient magnetic field generating coil

34: gradient magnetic field power source

40: transmission system

42: high frequency oscillator

44: modulator

46: high frequency amplifier

48: irradiation coil

50: receiving system

52: receiving coil

54: signal amplifier

56: quadrature phase detector

58: A/D converter

60: signal processing system

61: external storage device

62: optical disc

64: magnetic disc

66: memory

70: SAR calculation unit

80: bed control device

82: bed

84: top plate

90: input and output device

92: pointing device

94: keyboard

96: output device

98: display

99: printer

100: MRI apparatus

150: cursor

152: scan name

182: model image

190: bed input portion

192: operation button

262: reference marker

272: part marker

604: object information storage section

605: object information storage section

606: imaging condition storage section

607: imaging condition storage section

800: setting image

810: scan list display portion

820: selected imaging condition display portion

830: positioning image display portion

832: positioning image

834: scan position

836: scan position

838: imaging section

840: SAR value display portion

842: SAR value

844: specified SAR value

850: imaging parameter display portion

852: repetition time

854: echo time

856: bed position

860: imaging start mark

870: imaging schedule display portion

872: setting display

880: scan order candidate display portion

1. A magnetic resonance imaging apparatus, comprising: a bed including atop plate that moves an object placed thereon; a magnetic fieldgeneration means which generates a magnetic field in a space in whichthe object is located; an irradiation coil for irradiating the objectwith RF pulses; a means which detects an NMR signal generated by theobject and images the detected NMR signal; an input and output devicefor inputting or displaying imaging conditions; and a control devicethat calculates an amount of absorption of electromagnetic waves causedby the irradiation of the RF pulses to the object based on the inputimaging conditions, determines whether or not the calculated amount ofabsorption satisfies conditions of a specified value (SAR upper limit)of the amount of absorption of electromagnetic waves, and performsmovement control of the top plate and irradiation control of the RFpulses in accordance with imaging conditions determined to satisfy theconditions of the specified value (SAR upper limit) of the amount ofabsorption of electromagnetic waves.
 2. The magnetic resonance imagingapparatus according to claim 1, wherein the control device performsdisplay indicating that the conditions are not satisfied on an input andoutput device when the amount of absorption of electromagnetic wavesinto the object calculated in accordance with the input imagingconditions is determined not to satisfy the conditions of the specifiedvalue (SAR upper limit) of the amount of absorption of electromagneticwaves, when new imaging conditions are input, the control devicecalculates the amount of absorption of electromagnetic waves in a partof the object to be imaged or a bed position where imaging is scheduledand determines whether or not the calculated amount of absorptionsatisfies the conditions of the specified value (SAR upper limit)according to the newly input imaging conditions, and the control deviceperforms the movement control of the top plate and the irradiationcontrol of the RF pulses in accordance with the imaging conditions usedin calculation of the amount of absorption when the newly calculatedamount of absorption of electromagnetic waves satisfies the conditionsof the specified value (SAR upper limit).
 3. The magnetic resonanceimaging apparatus according to claim 1, wherein the control devicefurther includes a database of an absorption rate of electromagneticwaves that uses a part of the object to be imaged or a bed positionwhere imaging is scheduled as a search parameter, and the control devicereads an absorption rate of electromagnetic waves from the database withthe part of the object to be imaged or the bed position where imaging isscheduled as a search parameter, and calculates the amount of absorptionof electromagnetic waves in imaging in the part or the bed positionusing the read absorption rate.
 4. The magnetic resonance imagingapparatus according to claim 3, wherein a database (W-basic) of theabsorption rate of electromagnetic waves is data indicating anabsorption rate of electromagnetic waves of a standard person with apart or a bed position as a search parameter, data indicating theabsorption rate of electromagnetic waves of the standard person is readfrom the database (W-basic) with the part of the object to be imaged orthe bed position where imaging is scheduled as a search parameter, andthe amount of absorption of the object is calculated using the read dataof the absorption rate of electromagnetic waves of the standard person.5. The magnetic resonance imaging apparatus according to claim 4,wherein the control device stores position information for imaging inthe part of the object or the bed position as information correspondingto the standard person, converts the position information correspondingto the standard person into information corresponding to the object, andcontrols movement or stop of the top plate of the bed using theconverted information corresponding to the object.
 6. The magneticresonance imaging apparatus according to claim 1, further comprising: anelectromagnetic wave absorption calculation unit that calculates anabsorption state of electromagnetic waves based on electromagnetic wavesemitted to the object, wherein the control device calculates the amountof absorption of electromagnetic waves absorbed by the object in imagingof a part of the object to be imaged or in imaging at a bed positionwhere imaging is scheduled using a calculation result of theelectromagnetic wave absorption calculation unit.
 7. The magneticresonance imaging apparatus according to claim 6, wherein the controldevice stores the calculation result calculated by the electromagneticwave absorption calculation unit with the part or the bed position as asearch parameter and a database, and the control device searches for thedatabase based on the calculation result of the electromagnetic waveabsorption calculation unit with the part of the object to be imaged orthe bed position where imaging is scheduled as a search parameter, andcalculates the amount of absorption of electromagnetic waves into theobject using the search result.
 8. The magnetic resonance imagingapparatus according to claim 7, wherein, when there is no datacorresponding to the part or the bed position in the search of thedatabase based on the calculation result of the electromagnetic waveabsorption calculation unit with the part or the bed position whereimaging is scheduled as a search parameter, the control device performsa search based on another part or another bed position instead of thepart or the bed position and calculates the amount of absorption ofelectromagnetic waves into the object using the search result based onthe other part or the other bed position.
 9. The magnetic resonanceimaging apparatus according to claim 8, wherein the control devicecorrects a search result based on the other part or the other bedposition instead of the part or the bed position where imaging isscheduled, and calculates the amount of absorption of electromagneticwaves into the object using the corrected search result.
 10. Themagnetic resonance imaging apparatus according to claim 1, wherein thecontrol device performs display indicating that the conditions are notsatisfied on the input and output device when the calculated amount ofabsorption of electromagnetic waves into the object does not satisfy theconditions of the specified value (SAR upper limit) of the amount ofabsorption of electromagnetic waves, calculates the amount of absorptionof electromagnetic waves with new imaging conditions of a waiting time,which are input, and determines whether or not the conditions of thespecified value (SAR upper limit) are satisfied when the new imagingconditions for increasing the waiting time for imaging of the object areinput, and performs the movement control of the top plate according tothe waiting time, which is used in calculation of the amount ofabsorption satisfying the conditions, when the newly calculated amountof absorption of electromagnetic waves satisfies the conditions of thespecified value (SAR upper limit) of the amount of absorption ofelectromagnetic waves.
 11. The magnetic resonance imaging apparatusaccording to claim 10, wherein the control device performs control toreduce a moving speed of the top plate of the bed upon an increase inthe waiting time in the imaging conditions.
 12. The magnetic resonanceimaging apparatus according to claim 10, wherein, when a plurality ofparts of the object or a plurality of bed positions are input as partsor bed positions where imaging is scheduled, the control devicecalculates an imaging schedule to increase or decrease the waiting timeby changing an imaging order and displays the imaging schedule on theinput and output device.
 13. The magnetic resonance imaging apparatusaccording to claim 2, wherein the input and output device includes adisplay, and the control device assigns names to a plurality of parts ora plurality of bed positions where imaging is scheduled and displays alist of the names on the display when the plurality of parts or theplurality of bed positions are input, displays imaging conditions of thepart or the bed position of a selected name when a specific name isselected from the displayed list, newly calculates the amount ofabsorption of electromagnetic waves according to changed imagingconditions when the displayed imaging conditions are changed, determineswhether or not the newly calculated amount of absorption ofelectromagnetic waves satisfies the conditions of the specified value(SAR upper limit) of the amount of absorption of electromagnetic waves,and displays the determination result on the display.
 14. The magneticresonance imaging apparatus according to claim 2, wherein an inputdevice for inputting a part is further provided in a gantry or the bed,the input device provided in the gantry or the bed has a display of aplurality of part names that are imaging targets, and when a part nameis selected from a plurality of part names displayed on the input deviceprovided in the gantry or the bed, the control device stores theselected part name as the part to be imaged, calculates the amount ofabsorption of electromagnetic waves in imaging in the stored part, anddetermines whether or not the calculated amount of absorption satisfiesthe conditions of the specified value (SAR upper limit).
 15. A controlmethod of a magnetic resonance imaging apparatus including a bed havinga top plate that moves an object placed thereon, a magnetic fieldgeneration means which generates a magnetic field in a space in whichthe object is located, an irradiation coil for irradiating the objectwith RF pulses, a means which detects an NMR signal generated by theobject and images the detected NMR signal, an input and output devicefor inputting or displaying imaging conditions, and a control device,the method comprising: a first step of calculating an amount ofabsorption of electromagnetic waves into the object according to theimaging conditions; a second step of determining whether or not theamount of absorption of electromagnetic waves calculated in the firststep satisfies conditions of a specified value of the amount ofabsorption of electromagnetic waves; a third step of performing displayindicating that the conditions are not satisfied when the calculatedamount of absorption of electromagnetic waves does not satisfy theconditions of the specified value of the amount of absorption ofelectromagnetic waves; a fourth step of calculating the amount ofabsorption of electromagnetic waves into the object according to newlyinput imaging conditions and determining whether or not the amount ofabsorption of electromagnetic waves based on the newly input imagingconditions satisfies the conditions of the specified value of the amountof absorption of electromagnetic waves; and a fifth step of performingmovement control of the top plate and irradiation control of the RFpulses under the imaging conditions satisfying the conditions when theamount of absorption of electromagnetic waves based on the newly inputimaging conditions satisfies the conditions of the specified value ofthe amount of absorption of electromagnetic waves.